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2023-12-15
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2025-08-24
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Godspeed, Zenitsu

Summary:

Unlike canon, Zenitsu receives the news about Kaigaku before Kuwajima does. This changes things, but not everything.

In which I turn Zenitsu into the Flash (not literally).

Notes:

Welcome! Thank you for checking out my fic!
I noticed there aren't many fics about Zenitsu and his Gramps, so I wanted to remedy that. I started writing when I realized that Zenitsu might've had a happy ending in canon, but he might've always regretted being unable to save Kuwajima. Knowing that his family member died a slow and painful death while he couldn't do anything to stop it must've really hurt. Zenitsu's one of KNY's fastest characters (probably), but he was too late to even try. In canon, dude had 0% chance of stopping it. So now, I’ve made it so that he has a chance to do something about his Gramps’ death.

The timeline/timing of events and locations/distance in the fic are unclear, but this happens during Hashira Training. I'm also uncertain about which spelling I should use for characters' names (Tanjiro (wiki)/Tanjirou(ao3)). Let me know if one's better than the other.

(See the end of the work for more notes.)

Chapter 1: G

Summary:

Zenitsu finds out. Everyone but Kuwajima finds out.

Zenitsu runs.

Notes:

Godspeed: "An expression of good wishes to a person starting a journey" (Oxford). Also Zenitsu's extension of the first form of Thunder Breathing.

Posted 12/15/2023

(See the end of the chapter for more notes.)

Chapter Text

Zenitsu should have known. Perhaps if he had been a more diligent student, a stronger demon slayer, or a more filial child, he would have sensed something was wrong when he woke up that morning.

He didn't. He went about his day as usual, whining about Hashira Training. It was seriously inhumane! Zenitsu had no idea how anyone could handle the torture.

After a morning of screaming, flailing, sweating, drooling, and crying, Zenitsu flopped gracelessly next to Tanjiro and Inosuke. Mitsuri had been kind enough to allow her trainees a break. Zenitsu was going to make the most out of it. Absolutely nothing would make his drained muscles move. Even Inosuke, with his energy and enthusiasm to mow anything down, was panting in his boar mask. Tanjiro was inching toward their water supply.

It was peaceful despite the heavy panting, gasping, and moaning. The unholy cacophony created by the group of drained demon slayers was impressive, but Zenitsu was too tired to care about the noise despite his hearing. It was a bit depressing, Zenitsu thought, that he had gotten used to the manly grunts and groans of exertion. Where were the elegant ladies with their cute huffs and sweet noises? Zenitsu prayed a goddess would soon bestow upon him a blessing.

Instead, Zenitsu got a crow. He could hear a Kasugai crow coming from afar. The frantic cawing roused Zenitsu's interest, but considering all the Hashira around HQ, he figured it wouldn't be his business or anything.

That is, until he heard, "...Roaring Hashira... defect-... Upper Moon..."

Zenitsu shot straight up. Roaring Hashira? That had been Gramps' title from when he was a Hashira. Had he been attacked by an Upper Moon? Zenitsu paled. He remembered Upper Moon Three's devastating attacks. Gramps was strong, but he was retired and even Rengoku-san had...

Tanjiro, trembling from training, turned to look at Zenitsu. "Zenitsu? What's wrong?"

Zenitsu didn't hear him. He was listening to the crow.

"Roaring Hashira disciple defected! Kaigaku turned! Upper Moon…"

Zenitsu's whole world shook. By this time, Inosuke had joined in on Tanjiro's questioning.

Kaigaku... had become a demon? That grumpy bastard had... given up Gramps' teachings to become a demon? He'd learned so many Thunder Breathing forms, more than Zenitsu. He would've become a Hashira in time and made Gramps proud, unlike Zenitsu. After seeing all these Hashira in action, Zenitsu felt the gap between him and fulfilling Gramps' hopes widen.

Gramps. What would Gramps think? For all his nagging, Gramps genuinely cared about them. He was their master-

He was their master. He was Kaigaku's master. He was the master of a demon-slayer-turned demon.

He was going to die.



Tanjiro was worried. It had been a normal, but tiring day until Zenitsu suddenly sat up. Heck, it was a break during Hashira Training. Zenitsu would never move during a break. But he had moved. And then he had ceased all movement just as suddenly as he had started. Was he even breathing? Tanjiro wasn't sure.

He scanned the area, but everything seemed and smelled normal except for Zenitsu. Zenitsu smelt wrong. He was usually scared, but the scent he currently gave off was... something different. Even Inosuke had noticed Zenitsu's strange behavior.

Inosuke leaped toward Zenitsu and started shaking him. "Monitsu! What's wrong with you? Answer Tomachiro!"

Zenitsu, who had been hanging limply in Inosuke's grasp, made an indescribable noise. Tanjiro hadn't heard anything like it before but he instinctively felt that it was likely similar to the sound he made when he returned home that snowy day.

Inosuke looked scared. "H-hey, Zamitsu, say something."

Zenitsu moaned, "Gramps..."

Tanjiro's ears pricked up. "Gramps? Zenitsu, did something happen to Kuwajima-san?"

Zenitsu whimpered. "He's... he's gonna die!"

And on that lovely note, Zenitsu disappeared from their sight. Tanjiro blinked. Inosuke's hands were hanging in the air.

They stared at each other blankly. Inosuke sputtered. "Where'd that come from?"

Tanjiro frowned. "He must've heard something. I haven't smelled anything, but Zenitsu probably heard a Kasugai crow's message. Something must've happened to Kuwajima-san. We should go ask around and find Zenitsu."

Inosuke nodded, and the two of them dragged their weary bodies inside.



Inside the headquarters, nothing seemed out of place. Tanjiro and Inosuke headed in, hoping they’d find someone they could question. They hadn’t expected the Insect Hashira out of all the Hashira they could’ve bumped into at the entrance. She wasn’t even running her own training.

“Shinobu-san? What are you doing here?”

Shinobu blinked, surprised to see them. “Ah, Tanjiro-kun, Inosuke-kun, I was visiting HQ for a talk with Oyakata-sama, but I’m staying for the upcoming Hashira meeting.”

Tanjiro’s heart leaped. “Has something happened?”

Shinobu smiled. “A Kasugai crow just brought in some important information—”

Inosuke interrupted her. “What information?”

This time, Shinobu’s smile seemed a bit darker. “I’m afraid that this information isn’t meant for your rank—”

Inosuke interrupted her once more. “It’s important! Zenichi looked like he was gonna die, and then he disappeared!”

Shinobu’s smile had become more and more menacing due to Inosuke’s interruptions, but her facial expression reverted to concern upon hearing about Zenitsu. “What happened to Zenitsu-kun?”

Tanjiro leaped to explain before Inosuke further offended Shinobu-san or complicated the story. “We were on a break when Zenitsu suddenly shot right up. He looked out of it, and he didn’t respond until Inosuke shook him.” Tanjiro paused, worrying his lip. “He… he made this really weird noise.”

Inosuke nodded. “Yeah, he sounded like a dying animal!”

Tanjiro continued. “After that, he wailed that his Gramps was going to die before disappearing on us. I think that was the fastest Zenitsu’s ever moved. We didn’t even see him go.”

Shinobu had looked more and more grim as the explanation went on. “I think I know what happened.”

She shot a stern look at Inosuke, who had been about to interrupt again, before asking, “Zenitsu-kun… he uses Thunder Breathing, right?”

She received confirmation before somberly continuing. The following news caused Tanjiro to gasp, and Inosuke’s eyes, hidden under his boar mask, widened as well.

“We just received news that cultivator Kuwajima-san’s disciple defected and became a demon.”

Notes:

Thanks for reading! I hope you liked it. Chapter 2's coming in a moment.

Also, please do let me know if there are inaccuracies. I'm not really sure how KNY characters address each other. I'm going with Shinobu-san for the trio because Zenitsu once thought it and Kuwajima-san is a guess. Tanjiro also called Obanai 'Iguro-san' a lot in the final fight, so calling her Shinobu-san doesn't seem too weird considering they probably spent more time with her.
Also, according to the wiki, Kuwajima's title was Roaring Hashira, not Thunder Hashira. I just went with it because it sounds cool.

Man, Zenitsu's so relatable. Idk how slayers endured Hashira training.

Feel free to comment, ask questions, and chat!

Chapter 2: O

Summary:

Zenitsu is running. The Hashira meeting occurs, and decisions are made.

Notes:

Posted 12/15/2023

(See the end of the chapter for more notes.)

Chapter Text

Zenitsu couldn't hear anything over the roaring in his ears. He couldn't feel anything. He was weightless as he sped across the ground.

Zenitsu was running. Running faster than he ever had before. Why was he running? Zenitsu couldn't remember. All he knew was he had to get somewhere. He needed to get there before... before something happened.

He was a flash of light that devastated the surroundings. Dirt flew, the ground cracked, shrubs were uprooted, and angry farmers cussed him out. The demon slayer was akin to a natural disaster as he crossed acres of land.

Time flew as fast as Zenitsu's legs. As he drew closer to his destination, he grew familiar with his surroundings. Zenitsu was going to make it home. He was going to see Gramps. He hadn't seen Gramps since he left on his first mission. Was Gramps going to be happy to see him? Proud of him? Zenitsu didn't think he deserved it, but Gramps had always believed the best of him. Gramps would probably praise Zenitsu for saving people even if he had been a blubbery mess during the rescue.

He was going to save Gramps.



The Hashira meeting began shortly. Tengen was also present, and Ubuyashiki Amane was representing her husband. The atmosphere was tense. Tanjiro clenched his fist and sat stiffly. Inosuke seemed flexible as usual, but even he looked solemn due to the situation. Until this point, the Hashira and Ubuyashiki-sama had been discussing other matters, but Obanai brought up a new topic.

“Why are non-Hashira slayers here?” He directed a pointed glare at the two.

Shinobu spoke up. “Their presence relates to an issue on the meeting’s agenda.”

Amane acknowledged Shinobu. “Yes, their friend is a disciple of former Hashira Kuwajima-san who now acts as a cultivator for Thunder Breathing.” She glanced around the room. “We have received unfortunate news. Kuwajima-san’s first disciple, Kaigaku, has defected and become a demon.”

Various reactions expressing surprise, dismay, and anger occurred among the Hashira.

Sanemi gritted his teeth. “Bastard! At a time like this, he—”

Obanai interrupted Sanemi’s outburst. “I still don't see why they need to be part of this meeting.” He jerked his head at the two slayers.

Shinobu explained, “They’re close friends with Kuwajima-san’s second disciple, Agatsuma Zenitsu. Earlier, they informed me that Zenitsu-kun was acting abnormally, so I explained the situation and brought them here.”

Sanemi focused on one point. “What do you mean he was acting abnormally? Are we getting another traitor?”

Tanjiro had been awkwardly minimizing his presence throughout the meeting, but he saw red and erupted at this moment. “Zenitsu would never! He may complain a lot, but he’d never betray us! He’s loyal.”

Inosuke supported Tanjiro’s declaration with “Yeah! Zamitsu’s a crybaby and a coward, but he’s not weak!”

Before Sanemi could continue, Amane hushed the group. “No one is assuming anything.” She gave a stern look to the unruly people before continuing. “May I ask what happened to Agatsuma-san? Why isn’t he here?”

Shinobu glanced at Tanjiro, indicating he was to speak.

“Ah, I think he heard the Kasugai crow announcing the news during our break. Er, his hearing’s really good.”

Inosuke butted in. “Yeah, he was acting like prey, so I shook him! He made weird noises and ran off.”

Tanjiro added, “He cried that Gramps, er, Kuwajima-san, was going to die before disappearing. He seemed really worried… Is Kuwajima-san going to be okay?” Tanjiro looked around but saw a room full of grim faces. He gulped.

Amane carefully answered him. “It’s a great dishonor for a cultivator to have a disciple who willingly became a demon.”

Inosuke impatiently responded, “What does that have to do with dying?”

Giyu, who had been unobtrusively blending into the background until now, stared straight at Tanjiro and succinctly stated, “Seppuku.”

Inosuke frowned. “Why sappekku?”

When it looked like Giyu wouldn’t break the awkward silence that formed, Gyomei patiently explained despite the tears trailing down his face. “Kuwajima-san is a man of honor. He may commit seppuku to atone for his disciple’s actions.”

Ignoring Tanjiro’s distraught facial expression and Inosuke’s perplexedness, Obanai stepped in. “Regardless, we must decide on a punishment for the cultivator in case he doesn’t go through with it.”

Tengen grumbled. “I think the betrayal is punishment enough.”

Obanai shot him a fierce look. “We must follow protocol otherwise further rule-breaking will occur.”

Amane interjected before another emotional outburst could occur. “My husband has made a decision after considering the current situation.”

Before she could reveal the decision, however, a Kasugai crow entered the room with a bundle of letters. Amane opened it, scanning the first letter. “Earlier, Kocho-san requested that the corps locate Agatsuma-san. A kakushi stationed at Konda Village sent a message after hearing complaints from local farmers.” Her brows furrowed. “Apparently, someone has been tearing up farmland by running across it.”

She opened the second letter. “This is from a slayer in the next village over. A yellow blur, possibly Agatsuma-san, was seen blasting through Higi Village's main square, damaging it and frightening people.”

Amane quickly opened and scanned the remaining letters. “It seems that Agatsuma-san is running toward Kuwajima-san’s residence and causing a disturbance while doing so.” She looked up at the Hashira. “From this, we can confirm that the chances of Agatsuma-san defecting are low. He seems to be rushing to ensure Kuwajima-san’s wellbeing."

Mitsuri gasped in surprise. “Agatsuma-kun was here for my training earlier! To have passed Higi Village, he must’ve been going insanely fast! I certainly couldn’t get there by now!”

Tengen nodded. “For him to pass by Higi Village so soon after Konda, he must be going at a flashy speed.” The Sound Hashira frowned. “I could match his speed, but I am a god after all. The boy’s probably overworking his body right now.”

Shinobu agreed. “Especially if he just finished Mitsuri’s training and hasn’t rested.” She turned to Amane. “I propose that we immediately notify Kuwajima-san about the situation with Kaigaku and Zenitsu-kun. Regardless of how he reacts to Kaigaku’s betrayal, he should be prepared for Zenitsu-kun’s arrival.”

Shinobu cast her eyes downward. “Zenitsu-kun will likely need medical attention after running all the way there. His speed is incredible, but I doubt that his body can handle the intensity.”

Amane nodded. “Proposal accepted. We will also notify members along the route to keep an eye out in case Agatsuma-san fails to reach his destination and collapses.”

Notes:

Hint: At the start of the chapter, Zenitsu passed out while running lol Classic Zenitsu.

I did my best with characterization! I also tried to give each Hashira a turn to speak, haha. I have no idea what Amane would call Zenitsu. I went with -san over -kun because I thought she'd prefer the more formal one. I don't know what she'd call Shinobu either, haha. Let me know if you know! It's hard because I don't think they've ever interacted in canon lol.

I posted these 2 chapters today in honor of Honkai Star Rail announcing that they're giving away a free 5* character, Dr. Ratio. Well, I also wanted to test the waters and see if people were interested in the fic. Extra motivation would be nice.

Pfft, anyways, Chapter 3 will probably come soon! As stated earlier, I've written all but the last 2-3 chapters. Working on editing Chapter 3 right now, so it'll be posted soon. Within a week? No promises, but I'm pretty darn sure it'll be posted this month.

Chapter 3: D

Summary:

Jigoro's completely average day might be his last, but Zenitsu runs to prevent that.

TW: An attempt by Jigoro.

Notes:

“Kaigaku, I’m sorry I failed to guide you. I hope you find the happiness you desperately desired. Return to the right path and atone.”
“My dear child, I’m so sorry I have to leave you alone. You will achieve even greater heights for you are my pride and joy. Live a good life, Zenitsu. I love you.”

Posted 12/17/2023

(See the end of the chapter for more notes.)

Chapter Text

Jigoro was living an uneventful life now that his disciples had become demon slayers. Throughout his day, Jigoro would be reminded of them by various knick-knacks and remnants they left at the residence. The training dummy Kaigaku whacked endlessly, the tree that Zenitsu had been electrocuted on, and other traces reminded Jigoro that his children were out there slaying demons. Those brats… they hadn’t sent him a single letter. He hoped they were doing well and becoming stronger.

That evening, Jigoro finally received a letter about his disciples, but it wasn’t from them. The news was enough to make Jigoro drop his cane, and he collapsed to his knee.

Kaigaku… had defected? He was a demon?

Jigoro couldn’t think or breathe. Kaigaku had always been a brash boy, but he had always been determined to improve. He had trained hard to become a strong demon slayer. He wouldn’t do something as cowardly or foolish as becoming a demon. Jigoro reread the lines. They were unchanged.

The old man was stunned. He might’ve even proceeded to faint, but, in his disorientation, he managed to notice that Zenitsu’s name appeared in the next paragraph.

The cultivator’s heart shook.

His boy… sweet and caring Zenitsu… Had he been on the same mission as Kaigaku? Had his death led to Kaigaku’s choices? Jigoro knew the boys had a strained relationship, but in the end, they were brothers, if not by blood, but through his training. Perhaps Kaigaku had done it to save Zenitsu.

Either way, he hoped with all his heart that Zenitsu was safe. Hands shaking, he read the paragraph that contained Zenitsu’s name.

“Upon hearing of Kaigaku’s defection, Agatsuma Zenitsu abandoned Hashira Training. We believe that he is running to your location at extremely high speeds. Based on his progress, it is likely that he will arrive late at night or early in the morning. It would be wise to delay your actions concerning Kaigaku because Agatsuma will likely need medical attention. The Insect Hashira believes that the run will severely burden his body. Please prepare medical treatment for him and contact a doctor in case...”

Jigoro’s face crumpled along with the letter clutched in his hands. Zenitsu was alive. That silly boy was hurting himself to hurtle here and make sure an old man was fine.

Jigoro was grateful. Grateful that Zenitsu was alive, but also selfishly grateful that his child cared enough about him to drop training and instantly dash to his side even at the expense of his health.

Now, Jigoro knew what he had to do. Setting aside the terrible letter, the former Hashira rose. According to the letter, Zenitsu would likely arrive in a few hours. He had to prepare quickly.

After all, he could not die in front of his children.



Where was he? Was he dreaming?

Earlier, he had remembered something about Gramps… seeing Gramps. Was he going to see Gramps in his dreams? This couldn’t be real, after all. He’d never run so far or fast in his life… but he’d also never dreamed a dream like this before. They were usually slower and didn’t involve this much variety in terms of scenery: forests, villages, farmland, the ground rupturing beneath his blurry legs, and oddly enough, angry villagers.

They also hadn’t hurt this much before. The demons in his previous dreams cut, slashed, and tore at Zenitsu, but the pain from those wounds was incomparable to the all-encompassing pain Zenitsu felt right now.

His entire body was on fire. It was somehow worse than being struck by lightning. That, at least, had been quick. This, however, had been going on for ages. He felt everything but nothing all at once. His muscles were melting, but his legs were gone.

Zenitsu wanted to stop. He wanted to lie down and kiss the ground. He needed rest. If only the dream would end…

The blonde’s legs stuttered, and his body shook as he nearly stumbled. Maybe stopping would make the pain go away. He’d see Gramps tomorrow or something. He was almost there after all. He recognized those landmarks; he’d be seeing Gramps soon. It’d be fine. Zenitsu could rest.

Zenitsu slowed, but the pain didn’t decrease. Instead, the pain in his chest skyrocketed.

Zenitsu thought he must’ve clutched his chest, but he honestly couldn’t feel his body much, just pain. But why… why did this pain feel different? It was a different type of burn. The same type of burn he’d felt when he’d heard Tanjiro cry…when he saw Inosuke on the ground… when Rengoku-san had—

Zenitsu’s eyes shot open. He was in pain, but he was awake.

He absolutely couldn’t stop running. All the pain in the world wouldn’t stop him from saving Gramps. Gramps would not die tonight. Zenitsu wouldn’t allow it.

Ignoring his body’s complaints, Zenitsu pushed on even faster. He was almost there. He knew where he was, and he was close. Just a bit farther…

It hurt, and his vision was fading, but he could see the lights. Their home was in sight.

Zenitsu put everything into his legs and vanished into the light.



Jigoro was ready. In a way, he was at peace. He trusted that Zenitsu would meet his expectations and carry his hopes and dreams with him into the future. More importantly, he knew his child had grown to become an excellent young man with a strong heart and sturdy body. Jigoro hoped that Zenitsu knew he was proud of him, but he’d written a letter in case.

Furthermore, he had already contacted the nearest doctor, and they would be arriving soon to care for Zenitsu. Zenitsu would live a long and happy life.

Jigoro did not need an assistant. Finding one would waste time. If the delay caused Zenitsu to arrive at the moment, Jigoro would never forgive himself.

Jigoro readied his blade and knelt on the mat. He would slit his stomach to atone for failing Kaigaku. The ex-Hashira let out a breath and gripped his weapon tightly. His eyes closed. He thought of Zenitsu and Kaigaku.

He moved his blade.

Jigoro expected that he’d face death in a moment. He knew it would be a slow and painful one since he lacked an assistant. It would be worth it to spare Zenitsu the sight and atone for Kaigaku.

Yet, Jigoro opened his eyes once more to face a god. No, someone possessing the speed of one.

Notes:

To be clear, Jigoro did NOT finish reading the letter.

Wow, I'm absolutely delighted by the number of kudos/comments/bookmarks this fic has received! I really appreciate it, and it's motivated me to edit/write faster. My first fight scene is coming along painfully, but it's being written! I'm editing Chapter 4 as well, so it'll be out within the week hopefully. Maybe earlier, but we'll see. No promises as usual.

Also, I apologize for the cliffhanger XD I didn't realize I had so many early on... At least the tags are there to reassure you? To make up for it regardless, Chapter 4's almost double the length of my normal chapter length. It packs in a lot.

According to Wikipedia, seppuku usually happens with an assistant standing by to behead the person and shorten their suffering after they slit their stomach. I'm pretty sure that Jigoro died completely alone in canon. That just makes his death even more tragic, ya know? EDIT: Huh, Zenitsu actually explained that in the manga.
Anyways, the lines in the notes at the beginning were originally meant to be part of the chapter, but I wondered if I should let Jigoro's actions speak for his thoughts/emotions at that scene where he kneels. What do you think?

Lastly, I'd like to ask: How'd you find this fic? Like, what tags and searches? Did you find it through bookmarks or recommendations? I usually look through my favorite tags or people's bookmarks after I read a fic of theirs.

Chapter 4: S

Summary:

Highly charged conversations occur.

Notes:

They finally have a proper meeting! Hooray! It's a charged one. *winks
The first segment elaborates more on the previous chapter's last line. Jigoro's eyes start out closed and open after this chapter's first line. He doesn't open then close then open his eyes XD I hope I'm not making this more confusing by explaining lol

Posted 12/20/2023

(See the end of the chapter for more notes.)

Chapter Text

Jigoro felt the ground quake beneath him as a thunderous boom echoed throughout the room.

His eyes snapped open. The wall in front of him had disintegrated, but what caught his attention was the brightest light he’d ever seen. It was all he could see and feel. It was so intense it should’ve burned, but it was warm. It was familiar. So was the silhouette he was starting to see.

Zenitsu?

Was that… Zenitsu?

That was all he managed to think before the golden streak slammed into him. No, not him. His blade. His blade soared into the air and wedged itself solidly into the wall, but no one in the room had eyes for it.

They only saw each other.


Moments earlier


Wreathed in an aura of lightning, Zenitsu didn’t bother with the door. Opening it would’ve wasted time. If the delay caused Zenitsu to arrive late, he would never forgive himself. Zenitsu barely felt it as he collided with the wall. It crumbled beneath him, just as the ground and other buildings and trees had on the way here.

Zenitsu’s vision was going, but he instantly zeroed in on his Gramps and, more importantly, the blade about to slash at his stomach.

Thunder Breathing First Form: Thunderclap and Flash - Godspeed!

The blade was no match for Zenitsu. He knocked it out of Gramps’ hand, removing it from the equation and only leaving them.

Zenitsu finally stopped running, but he couldn’t stop yet. He gasped, eyes blown wide-open, heart pounding feverishly, and made eye contact with his stunned master.

"You can’t die, Gramps!" He choked out, panting heavily.

Jigoro’s empty hand slowly extended, reaching out to the exhausted slayer. He began, “Zenitsu—"

Zenitsu cried out, “Shut up! I don’t care about honor or duty! You can’t die!”

They stared at each other silently. Zenitsu could see that his grandfather’s resolve hadn’t wavered, and Jigoro could see Zenitsu’s determination despite his shaky state.

The stalemate had to break. Zenitsu bit his lip, almost drawing blood. He clenched his fists, or at least attempted to, and declared with all his heart, “I swear… I’ll follow you if you do! You- you gave me everything—you’re everything to me!”

Jigoro attempted to speak, but Zenitsu stumbled forward. The ex-Hashira reached out to steady him, but Zenitsu’s legs finally gave up on him. He knelt and faceplanted into Jigoro’s shoulder. Jigoro’s arms wrapped around his child, and Zenitsu weakly trembled in his arms.

Just now, Jigoro had seen how magnificent Zenitsu’s aura had become, but at this moment, the young slayer still felt like a small child. It reminded Jigoro of the young boy he met on that fateful day on the street. It might’ve been years since then, but Jigoro experienced anew the same feeling of being needed and needing.

Softly and plaintively, Zenitsu whispered into his shoulder, “Please don’t leave me alone…”

Before Jigoro could react to his child’s heart-wrenching plea, Zenitsu truly collapsed. He went limp in Jigoro’s arms, and Jigoro’s heart nearly stopped.

Jigoro stopped himself from panicking and checked for a pulse. It was very slow, alarmingly so. Zenitsu’s body was warm enough to hurt, and he was drenched in sweat and covered in dirt. His ankles were bloody, and his shoes were soaked in blood. His clothing was in rags, and his golden hair was matted. He was still like death.

The ex-Hashira checked the time. The doctor wouldn’t be arriving for a few hours. Zenitsu had been quicker than HQ or he had expected.

Jigoro left Zenitsu, but this time he left to find help.



“-enitsu…”

 

 

 “How unflashy.”

 

 

 “This kid—”

 

 

“Chirp!”

 

Was Zenitsu dreaming? He could make out voices, but unlike his usual dreams, he couldn’t hear much. Chuntaro’s chirp reassured him that he was safe though. Perhaps he could stay in the warm darkness.

 

 

“…up soon, plea—”

 

 

“-kay, right?”

 

 

“—chu, fight me!”

 

 

“Your gramps is—”

What about Gramps? Had something happened to him? Gramps was super strong. What could possibly hurt him? Besides, Gramps was retired. There was no way he could die. Right?

Zenitsu was the one who was going to die. He’d end up as some demon’s meal or something. Heck, right now he was probably at the Butterfly Mansion because of some injury. That’d explain the feeling of safety and why his limbs felt like lead. The voices though… they hadn’t sounded very feminine, at least most of them hadn’t. Even in his dreams, Zenitsu couldn’t hear the dulcet tones of beautiful ladies. Instead, he heard the ravings of idiots and old men.

He didn’t want to wake up to men. He wanted to open his eyes to see fair women. It was easier being asleep. It was quieter, less scary, and there were fewer expectations, but Zenitsu felt a pang of guilt. Staying asleep meant letting down Gramps, who had given him everything and meant everything to him.

Huh? Zenitsu had never really expressed how much he loved his Gramps because it was too awkward, but somehow those words had felt familiar. Was he forgetting something?

“…You- you gave me everything—you’re everything to me!”

Zenitsu’s chest hurt. He remembered Gramps…and Kaigaku. Even if Gramps was dead, at least he’d managed to tell Gramps how much he meant to him. Zenitsu might’ve been slow as usual, but he hadn’t been completely useless this time. All the running had accomplished something. Even if he had failed in the end.

Running? So that was why his legs hurt hellishly. He hadn’t been injured by a demon this time. No, it had been himself. He had been willing to give everything to save Gramps or at least see him one last time.

Now Zenitsu didn’t want to wake up for a whole new reason. If he stayed like this, he could believe that Gramps wasn’t dead… that he had succeeded for once. That he wasn’t a failure when it mattered the most.

 

“Thank yo—”

 

“…my pride an—”

Zenitsu struggled. He had to know. Even if Gramps was gone, Gramps would’ve wanted him to be strong and fight alongside his friends. He wanted Gramps to be proud of him even in the afterlife. He would do this. Zenitsu would wake up.

Eventually. He’d get there eventually. Gramps believed in him after all.



Everything was muffled. Zenitsu couldn’t hear like usual, and his entire body was sore. Moving would hurt, but Zenitsu slowly cracked an eye open. He knew that ceiling.

Butterfly Mansion.

He opened another eye. Zenitsu tried opening his mouth, but it was cemented shut. He tried again.

“Wa—water…” he croaked.

Someone lifted a glass to his lips, and he sipped eagerly before it was taken away too soon. Slightly rejuvenated, Zenitsu’s sight and hearing slightly cleared. Aoi was peering at him with a look of concern. Wow, he was so lucky. He’d woken up to an absolute goddess after hearing all those deep voices. Deep voices?

Zenitsu wiggled fruitlessly in place. “Gramps!” He shouted as much as his cracked throat would let him. “Where is he? Is he alive?”

Aoi shushed him. “He’s fine. He’s been sitting next to you waiting for you to wake up, slowpoke.”

Zenitsu’s eyes watered. “He’s alive?” The tears started flowing. “I…made it?”

Aoi rolled her eyes but smiled fondly. “He’s completely fine. You did it.”

Zenitsu smiled despite the pain. “Where is he?” He struggled to move his head, but Aoi stopped him.

“We managed to convince him to stop camping here. Kuwajima-san is eating lunch. I promised him I’d sit with you while he ate.” She paused. “He should be here soon. It’s been a while.”

Zenitsu relaxed into the bed and shakily nodded. “That’s… that’s good.”

Aoi then grumbled, “As for those two goofballs of yours, they also made a nuisance of themselves hovering around you until they were sent on missions. They’re on one right now.”

Aoi then proceeded to update Zenitsu about his current state. Apparently, he had badly torn up his body with his marathon. He had been unconscious for weeks. Zenitsu squeaked when he heard how his heart had briefly given out. Overall, he would be on bed rest for a few more weeks.

Zenitsu frowned, causing Aoi to gently smack him on the head. “Ugh, you have no idea how worried everyone was! They were so annoying! Even the former Sound Hashira stopped by to visit, you know. Be glad that you won’t have permanent issues after going overboard like that.”

Zenitsu reluctantly agreed. He hoped the pain wouldn’t stay like this the whole time though.

Before Aoi could scold him more, the door opened. Zenitsu tilted his head towards the doorway.

It was the best thing he’d ever seen. Gramps was silhouetted in the doorway. Zenitsu could hear his loud heartbeat beat as firmly as ever. Gramps was alive. Zenitsu wasn’t a failure after all.

He choked out, “Gramps!” before arms were gently embracing him. He sniffled and leaned into the hug more even though his body still hurt. Gramps was warm. Zenitsu had never felt safer.

“Zenitsu…” Gramps trailed off. Zenitsu peered through his tears to look at him.

“Zenitsu, YOU FOOLISH BOY!” Gramps roared. Zenitsu and Aoi flinched. Aoi slowly inched out the door, knowing that an intense conversation was about to occur.

“You shouldn’t have torn up your legs like that! How are you going to use Thunder Breathing if you destroy them? How many times have I told you to take care of your legs!”

Zenitsu wailed, “I’m sorry, Gramps! I—”

He paused. He had been about to say that he hadn’t meant to, but that wasn’t entirely true. He had been willing to sacrifice everything for Gramps.

Zenitsu gulped. “I don’t regret it.”

Jigoro looked angrier, but Zenitsu continued before his scolding could resume. “I meant what I said earlier. You mean everything to me, Gramps.” The youth choked back a sob. “Even if I never walked again, never slayed a demon, and never became a Hashira, I wouldn’t ever regret it.”

Zenitsu saw as his Gramps’ angry façade melted, and what Zenitsu saw next made him want to cry harder. Gramps looked sad and old. He looked tired and pained. He looked conflicted and guilty, but most of all, he looked like he loved Zenitsu.

He sighed. “You silly boy… Don’t ruin yourself for an old man like me.” When Zenitsu began to protest, the ex-Hashira cut him off.

“Zenitsu, I’ve always wanted the best for you. From the start, I knew you had great potential. Training you might have been the most difficult thing I’ve ever done, but I don’t regret picking you up that day. You’re my child, so naturally I want you to live well and not be burdened by me.”

He gave Zenitsu a firm but wet look. “You shouldn’t have pushed yourself to stop me. I would have been following my duty—”

“BULLSHIT,” Zenitsu roared. He sat up, ignoring his injuries. “Gramps, dying would have done nothing! Forget about stupid honor, your death wouldn’t have meant anything to that bastard, and screw the corps! You shouldn’t have to die because of stupid Kaigaku or dumb rules!”

He jabbed his finger into Gramps’ chest. “You’re the silly one!” Zenitsu sputtered, “You-, you-, you…” and broke into tears again. “You,” he sobbed, “would’ve left me…”

He clutched Gramps tighter, and Gramps returned the hug. Tears ran down both of their faces.

“I’m sorry, Zenitsu.”

“Don’t go…please.”

Notes:

Man, convos are hard to write. Especially the emotional ones. I hope I did okay... Let me know what you think!
Anyways, they're not quite done talking yet, but at least it ended well (for now).

I usually aim to write 1k words for a chapter, so I delivered on what I said in last chapter's notes! This is almost 2k. And no cliffy? Kinda? Things are up in the air, but at least no one's dying, right?

I also wanted to say that Jigoro saw a color (not just light), but... Zenitsu's Thunder Breathing color... is complicated? Blue with some yellow in the anime, yellow in the manga apparently. I just omitted it lol because I couldn't pick. :P
Note that the first segment of this chapter also probably happened in like... seconds or less. Zenitsu was in speedster mode, but I reasoned Jigoro could see him fairly well in that split-second since he's a Thunder Breathing master.
Also, Zenitsu was too exhausted to hear what people were saying/doing. Have fun figuring out who was at his bedside!

Demons weren't active around the Hashira Arc...but let me have missions, please. It's canon divergence, after all. Let's just say that there were a few missions that lower-ranked slayers were still sent out on. Extra training! XD
Also, I know that Hashira Training had an order, but we're going to be flexible, right? Thanks. :3

Chapter 5: P

Summary:

Decisions get made, Zenitsu trains, and retired Hashira bond.

Notes:

Uzui Tengen finally makes a more significant appearance! It's not much, but he'll play a bigger part in later chapters. Also, I know that his training was technically first in Hashira Training, but this is an AU. You can rationalize it as Zenitsu going back for more stamina/running training or just the order being different than in canon. Thanks for understanding!

Posted 12/23/23

(See the end of the chapter for more notes.)

Chapter Text

Days passed, and Zenitsu slowly became more mobile. His entire body still hurt, but he could sit up at least. He still slept a lot, but he was able to hold longer conversations, no longer falling asleep like he had during his tearful conversation with Gramps.

Both Tanjiro and Inosuke had been relieved to see Zenitsu was awake. Tanjiro had updated him about Hashira Training, and Inosuke had challenged him to a fight once he was better. They accompanied him as long as they could, but with Hashira Training and missions, they were busier than ever. Zenitsu didn’t begrudge them for that and often shooed them away to do their own things.

It was difficult facing Gramps though. Even after their charged conversation vented some of their emotions, they were still awkward. Zenitsu worried that Gramps was still intent on seppuku, and Gramps… who knows what he was feeling. Zenitsu knew that Kaigaku’s betrayal was even harder on Gramps. To Zenitsu, Kaigaku had been an annoying and irritable senior, but Gramps had picked Kaigaku and trained him as his successor. He had been especially proud when Kaigaku passed the selection.

Zenitsu didn’t want to confront Gramps about it, but he couldn’t have Gramps’ life hanging in the air. It took him a few more days, but he soon resolved himself. He knew what he had to do.

The blonde spoke up one day when the old man was peeling apples by his side. “Gramps, let’s talk.”

Kuwajima looked up at Zenitsu and recognized they were in for a serious conversation. He set down the knife and apple. “What is it, Zenitsu?”

Zenitsu steeled himself. “Don’t die,” he stated calmly.

Staring into Gramps’ eyes, Zenitsu saw that he was about to use the same argument about honor and duty, so he stopped him. “Atone another way.” Gramps looked surprised, but Zenitsu continued before he could ask.

“Stay with me, Gramps.” Zenitsu resolutely made eye contact with Kuwajima.

“Stay by my side as I train and become a Hashira,” he declared. “I’ll defeat enough demons, and…” He took a deep breath.

“I’ll defeat Kaigaku. You won’t need to commit seppuku because I, as your disciple, will reclaim your honor for you.”

Zenitsu took Gramps’ aged hands into his own and clasped them firmly. “You’ve done so much for me. I won’t disappoint you this time, Gramps.”

This time, Zenitsu’s eyes stayed dry while Kuwajima’s started tearing up. The old man wiped his eyes before smiling at Zenitsu with an expression full of love.

“Zenitsu, you have never disappointed me. You don’t need to become a Hashira to make me proud. After all…”

Zenitsu’s heart pounded hard enough to deafen even him, but he heard the following words loud and clear. He would remember them forever.

“You are my pride and joy.”



After Gramps force-fed him the apples, Zenitsu made sure that Gramps would not be committing seppuku. It ruined their emotional moment, but Zenitsu badgered him enough to extract a promise that he wouldn’t commit seppuku even if the corps asked for it.

In exchange, Jigoro requested that Zenitsu become stronger while doing his best to stay alive. He also set a deadline. The wise old man cared for Zenitsu’s well-being and knew that seeking revenge could ruin a person, so he stated that Zenitsu would have to accomplish his goal within a year. If he didn't succeed by then, Zenitsu would give up on defeating Kaigaku.

Both of them ignored what might happen if Zenitsu failed, and Zenitsu fervently guaranteed he would succeed within the timeframe.

Jigoro didn’t tell Zenitsu that the letter from HQ hadn’t demanded his death as punishment. During Zenitsu’s time being unconscious, he had finished reading the letter. Apparently, his ability to train slayers was far too important at this crucial point, so he would make up for his failure by acting as an assistant during Hashira Training. Oyakata-sama had also hinted that he would accept Zenitsu’s future successes as atonement. According to him, one failure did not mean Jigoro was a failure, especially since his other disciple was loyal and flourishing into an excellent slayer.

Jigoro kept this from Zenitsu because he knew Zenitsu needed the extra pressure. The ex-Hashira understood that Zenitsu’s chances of defeating Kaigaku and living would drastically decrease once Kaigaku mastered his abilities and adapted to being a demon. Kaigaku had never mastered the first form of Thunder Breathing, but he had been a strong slayer and would likely become a strong demon. It was entirely possible that he would reach the level of the Lower Moons, perhaps even the Upper Moons. Zenitsu would have to become strong enough to defeat him before that happened. It was a race.

The old man wasn't happy that Zenitsu would be pressured by the time limit, but he knew that Zenitsu was meant for greater things than revenge and atoning for Jigoro’s failures. Even if he didn't defeat Kaigaku, Zenitsu’s path was not meant to be blocked by the failings of Kaigaku and Jigoro. Besides, Jigoro was confident that Zenitsu would be able to turn this old man's failure into strength and character development, and he knew deep down that Zenitsu would succeed.

After all, Zenitsu had already grown up. During his time at the Butterfly Mansion, Zenitsu’s young friends, particularly the boar-masked one, had regaled him with tales of their exploits. Zenitsu had met two Upper Moons and survived! He had slayed tricky demons and even contributed to the slaying of Upper Moon 6 and Lower Moon 1. Zenitsu, as Jigoro had expected, had become a splendid young man although he had still kept his tendency to cry and whine according to Zenitsu’s friends.

Surprisingly, the crying and whining had ceased. It had been replaced with a burning determination to get stronger. Once Zenitsu recovered and finished rehabilitation training weeks later, he began to constantly train. Jigoro supervised his training and gave small tips, but he had already taught Zenitsu as much as he could before the Final Selection. It was all up to Zenitsu now.

Zenitsu partook in Hashira Training, but he also did his own independent training despite Hashira Training leaving the other slayers downed.

Jigoro could tell that the hard training was effective and Zenitsu was growing stronger rapidly. This came at a cost, however. In the past, Jigoro had nagged Zenitsu because the boy did everything to avoid training. He had literally set traps to catch Zenitsu when he fled due to training. Now, Jigoro was pleading for Zenitsu to take breaks.

Zenitsu always did once Jigoro asked because he couldn’t refuse the look in Gramps’ eyes, but he made up for it by sneaking out and training more at night. Naturally, this meant he lost sleep. That had consequences.

One day when Jigoro was giving tips to some slayers who were taking part in Hashira Training, the retired Sound Hashira stomped up to him. He was dragging a sleeping Zenitsu. The trainees quickly bowed and backed away before fleeing.

Tengen roughly dropped the blonde onto the floor in front of Jigoro. “Kuwajima-san, take better care of your disciple. The brat’s been falling asleep during my training. He's been running while sleeping, and it’s distracting the other slayers.” He exasperatedly dragged a hand through his white locks. “He’s not going to learn anything flashy from me if he’s asleep, and the others aren’t paying attention and running properly because they’re too busy gawking!”

Jigoro coughed, embarrassed. “Apologies, Uzui-san. I’ve wrangled him into taking breaks, but I haven’t caught him every time he’s snuck out at night to train. I’ll make sure he rests properly from now on.”

Tengen sighed. “I understand.” He also glanced at Kuwajima before muttering, “Don’t be ashamed of the kid though. He’s a good one. He’ll survive.”

Jigoro laughed. “You don’t need to tell me that, Uzui-san. I already know it.” He smiled at Tengen. “Thank you for guiding my foolish disciple.”

Tengen briefly looked away before grinning broadly at the old man. “Hah, he sure needed it! Have you heard about his mission with me in the entertainment district? The flashiest thing about him is his skill with the shamisen!”

Jigoro raised an eyebrow. “I’ve heard about it from his friends who accompanied him, but I’d be interested in hearing what happened from you, Uzui-san. It was impressive how you defeated Upper Moon 6, especially since the fight was in a crowded area.”

Tengen nodded. “Let’s go inside. Then…” The former shinobi struck a flashy pose. “I will regale you with the tale of our flamboyant takedown of Upper Moon 6!”

The two retired Hashira entered HQ. Jigoro remembered to drag a sleeping Zenitsu inside with them but only barely.

Notes:

You have no idea how many times I typed Kuwajiro instead of Kuwajima in this fic. XD I hope I caught and fixed them all... let me know if some snuck in lol.
Uzui will also play a larger role later in the fic, so if you're here partially for Uzui & Zenitsu... please wait patiently. XD Also lmao, just realized the height difference at the end there. Tall and small retired Hashira XD

Btw, thanks for all the kudos/comments/bookmarks/subscriptions/hits! They really motivate me, and I'm going alkdjflkafdjksl because I've never gotten this much engagement before.

The following two chapters include extras from a variety of POVs! Instead of reading about Zenitsu training, you get extras and a timeskip! Don't worry, the extras will still be about Zenitsu (our MC) though. Some include canon characters while others include Outsider POV.
Also, don't worry if you don't like OCs because they'll have a really small role (just in the extras for Outsider POV) and never appear again afterwards.

Chapter 6: E

Summary:

1. The series of events that led to the kakushi messaging HQ about Zenitsu. Set during Zenitsu's run.
2. The series of events that led to the slayer messaging HQ about Zenitsu. Set during Zenitsu's run.
Also known as: Zenitsu's run ruins and saves some lives.

3. Aoi has a fright at night. Set shortly after Zenitsu woke up at Butterfly Mansion.
4. Zenitsu gets bonked ft. Tanjiro & Inosuke. Set right after Zenitsu recovered.
Also known as: Zenitsu suffers in a good way.

Notes:

E is for extras! Let's start the year with something happy.
Crack Treated Seriously goes hard in this chapter.
The Outsider POV and OCs are only in the first two extras and won't show up again in the fic.
It's a longer chapter, so enjoy! I hope you like at least one of the extras. They're more lighthearted than most of the story. Lemme know if you have a fave!

Posted 1/1/2024 (Happy New Year!)

(See the end of the chapter for more notes.)

Chapter Text


1. An Unnatural Disaster 


Densuke’s back complained as he hefted his tools. He had spent his morning working his field outside of Konda Village. He longingly gazed at the village, which he could see in the distance. Today’s work had been especially tiresome, so he deserved to head back for a meal. The middle-aged man cast his eyes around for his nephew, Takeru, who had been working with him today.

Takeru was a foolish youth with a head full of fantasies. The teen constantly claimed that he was going to accomplish some heroic feat using the unusual ability that he had been blessed with. Densuke acknowledged that Takeru’s eyesight and reflexes were unnaturally good, but the boy clearly needed to be kept on the right path. It was worrying that Takeru had taken to bothering demon slayers who stopped to rest at the village for stories.

Every villager knew Takeru admired demon slayers and wanted to be one. Densuke had been about to tear the rest of his thinning hair out when a passing slayer had reciprocated Takeru’s interest due to Takeru’s keen eyesight and fast reaction time. Thankfully, Takeru had some common sense and responsibility, enough to recognize that he couldn’t run off and become a slayer without leaving his mother and younger sister to fend for themselves. The family was already struggling after losing Densuke’s brother last winter.

Densuke waved for Takeru to come closer. “Let’s go back for lunch. My treat. A reward for the work from this morning.” The man grunted. “Not bad.”

Takeru bounced in place excitedly. He ran to collect his tools before returning to his uncle’s side. The two began walking toward Konda when everything went wrong.

Densuke’s precious crops… his fertile farmland… his livelihood… had been ruined in a blink of an eye. The middle-aged man had no chance of preventing the massive line of devastation that crossed the entirety of the field. He hadn’t even seen what had happened because the sudden force that passed by had caused him to instinctively shut his eyes. It had all been over by the time he opened them again.

Densuke gaped at his ruined field. He had no idea what had happened just now, but his perfectly cared-for field had become divided by a crack in the ground. The crops around the massive rupture had been torn up and sprayed across the field.

He turned to look at Takeru. The boy’s jaw was similarly down, but his eyes were sparkling as he stared off into the distance.

“What was that?” Densuke slowly asked.

Takeru’s eyes refocused and his jaw snapped shut before he exclaimed. “That was so cool!” The idiot babbled, “Did you see him? That was the fastest I’ve ever seen anyone move!”

Densuke focused on the important parts. He’d teach the kid a lesson later for having the audacity to admire the asshole who razed his field.

“What person? Did a person do that?” The frustrated man shook his nephew. “What did your damned eyes see, brat?”

Takeru sobered up, realizing what the damage to their fields meant for them. He sheepishly said, “It was a person, uncle. A boy? No, a young man! He had the weirdest hair; it was yellow!”

Densuke was still pissed off. He roared, “And? What’d he do to our field? Why’d he ruin it?” 

The youth shrugged. “I think he was just passing by? All he did was run across the field.”

Takeru’s voice still contained awe as he spoke, “He was super fast! I can't believe he did all that by just running past us!”

Densuke smacked the youth. “Don’t admire the hooligan that ruined our fields! Don’t you know what this means for us? Months of work, GONE! We’re going to have to replant and pray!” The man’s hands flexed erratically in the air as if he were choking the criminal who ruined his field.

Takeru spoke up, “We should go ask the slayers—”

“Shut up about the slayers! We need to fix this!” Densuke shouted.

Takeru, the damn punk, pouted. “Yeah, but maybe they’d be able to compensate us for it. That guy had a sword. And only demons or demon slayers could move that fast.”

The brat added smugly, “Even with my eyes, I could barely see him! You were looking right at him before you blinked, and you saw nothing.” 

At least Densuke had a target now. “It was a slayer?” He grumbled. “Makes sense. A normal human couldn’t have done all that in a second.” He glared at his damaged field and rolled up his sleeves, revealing muscled arms.

“Nothing we’d do here would make much of a difference now, so let’s go give those bastards a piece of our minds. Some of the masked ones were here earlier. Let’s see if we can find them.”


2. A Blessing in Disguise


Higi Village usually didn’t have people guarding its gates. In actuality, the two downtrodden men loitering near the gates weren’t actual guards. They were slayers who had been assigned a mission to slay a demon hiding in the village. The demon was a weak one, but it had been abnormally difficult to track, so the two low-level slayers had already been stationed at the village for a few weeks.

Earlier in the day, they’d received a message asking them to notify HQ if they located a slayer. Some guy named Agatsuma who had blonde hair.

About an hour ago, a kakushi had sent them a message asking them to accost an incoming Agatsuma who had apparently vandalized some fields in the next village over.

Bored, the two slayers had decided to wait at the gates. The sun hadn’t set, so the demon they were looking for wouldn’t be out and about yet. Maybe they’d get a reward for stopping the other slayer.

Yasumoto yawned. “What do you think HQ wants him for? Their message came way before the one about the fields.”

Imatani shrugged. “Maybe he went rogue or something? Got fed up with Hashira Training?”

Both of them shivered. They’d quickly given up on Hashira Training and accepted this mission instead. Sure, it was boring being stationed in this dull village, but at least they weren’t being tortured.

 Yasumoto chuckled. “I wouldn’t blame him for that.” The swarthy slayer checked the time.

“We should head in and patrol if he doesn’t show up soon. It’s almost dark.”

Imatani nodded. “We don’t even know if he’s coming this way. The kakushi said that some kid in Konda saw him headed in this direction, but who knows,” the slayer concluded with a shrug.

Yasumoto opened his mouth to reply but sputtered as dirt and dust splattered into his face. Simultaneously, he felt the ground shake as he heard a deafening sound. When he managed to clean and open his eyes, he saw that Imatani was similarly disheveled.

The wooden gate they’d been standing next to had splintered and cracked as if something had blasted through it. The stunned slayers watched as it finally collapsed onto the ground with a loud thud.

“What was that?” Yasumoto cried, gesturing with his unsheathed sword. “A demon?”

Imatani rolled his eyes. “The sun hasn’t completely set yet, fool.” The slayer calmly sheathed his weapon, which he had also instinctively pulled out when the gate had exploded. “Stop waving your sword around.”

Yasumoto blushed and sheathed his sword. “Yeah, yeah, don’t start nagging.”

Imatani ignored him. “It was obviously that Agatsuma guy. The kakushi’s message mentioned that he tore up the fields somehow.” The calm demon slayer pointed at the gate.

“He probably blasted through them like he did to the gate.”

Yasumoto suddenly paled. “We gotta get away from here.”

Imatani shot him a confused look. “What?”

Yasumoto started pulling the smaller slayer into the village. “We’re the only ones nearby! The villagers are gonna blame us for the gate!”

Imatani yanked his arm free. “Okay, okay, let’s follow the trail he left. Maybe we can see where he’s going since I doubt we can catch up to him.”

Yasumoto whistled. “He sure was fast. Didn’t even see him.”

“Yeah, Thunder Breathers are like that. I heard something before he blasted the gate, but I couldn’t react at all.”

The two followed the trench in the ground deeper into the village. Imatani wondered why no one had come to investigate the shattered gate. It had broken with a spectacularly loud crash.

Imatani’s question was answered once they reached Higi’s main square. It was Market Day, so some chaos was expected, but this was different.

The ground was as torn up as the trail they had followed, but the people were the real issue. It was almost a riot, and the number of villagers lying on the floor was unusually high. People were wailing and shouting at each other. Produce and belongings were strewn across the floor, and some of the stalls had even collapsed. No one seemed severely injured, perhaps bruised or shaken at most, but Higi’s villagers were definitely upset.

There was an especially distressed crowd huddled around one collapsed stall, so the two slayers cautiously approached the group and listened in. The crowd seemed to be centered on the woman making a fuss on the ground in front of where the stall had been.

The young lady was inconsolable as she wailed. “Wa… wa….. Washizu-san!” She sobbed. “He…he’s gone!”

An older woman patted her back and attempted to soothe her, but a middle-aged man bluntly asked. “What happened to him?”

The lady choked out, “He disappeared! I don’t know what happened, but the stall collapsed and he…” She whimpered. “He melted!”

The slayers shot a look at each other. Could it have been…? They shoved their way closer to the crowd’s center to hear better.

The man looked unimpressed. “What do you mean he melted?” He turned to another person in the crowd. “Is she insane?”

The young woman shouted, “I’m not insane! I really saw it! It was like he was…” She wrung her hands. “…cremated on the spot!”

Yasumoto prodded the villager next to him. “Who’s Washizu?”

The villager shrugged. “Just an old man who set up a stall here every Market Day. He was popular because he gave treats to the kids. Some women liked him too because he gave them freebies sometimes.”

The sobbing lady must’ve heard their conversation because she tearfully added, “Washizu-san was a kind old man! He— he didn’t deserve whatever happened to him.”

Imatani internally groaned. Explaining that Washizu had been a man-eating demon would not go well right now. Washizu must’ve been the demon they’d been hunting. Who would’ve thought that a demon would set up shop during daylight hours? The stall’s overhang must’ve protected the demon from the sunlight while it masqueraded as a kind old man and gained its targets’ trust. What an abnormally bold and wily demon. No wonder it’d been hard to find.

The slayer sighed. Cleaning up this situation would be a pain for the corps. A slaying that took place at a village’s main square on Market Day? At least Agatsuma had been quick enough to leave the entire square confused. Maybe the corps would be able to avoid or deny any involvement since it seemed that no one besides them actually knew what happened to the square. Some villagers were already chalking it up to a natural disaster while others claimed it was a sign from the gods.

Yasumoto, meanwhile, was internally cheering. That Agatsuma guy had actually helped them out! His explosive dash through the square had collapsed the demon’s stall, bringing down the stall’s overhang and suddenly exposing the demon to sunlight.

The slayer cackled on the inside. How hilarious; the demon probably hadn’t even reacted before it died. It must’ve been so confused when it suddenly burned up. Had Agatsuma done all that on purpose? Or had it been an accident? The slayer looked around at the chaotic square. Hmm. He had to meet the guy someday. Agatsuma might’ve set a record for the fastest and most public slaying ever.

More importantly, they’d probably be able to leave now that the demon had finally gotten what it deserved. Yay!


3. A Midnight Horror Story


Aoi shivered as she headed to her room. She had just finished her shift, and it was late at night. Everyone was asleep, but perhaps this was the time when ghosts came out.

Recently, she had been hearing rumors that the Butterfly Mansion had become haunted by the ghost of a demon slayer who had died during a procedure. This wasn’t the first time the injured slayers had spread rumors about ghosts, but even the kakushi had begun to talk about this ghost. They claimed that they had heard the shuffling and pained groans. One brave slayer even boasted that they had run toward the noises to check but had seen nothing but an empty hallway.

Aoi cautiously walked through the dark halls. She didn’t believe the mansion was haunted, but she still felt scared, alright? It was completely normal to be a little nervous in a dark hallway. Aoi turned the corner.

A resounding scream rang through the hallways of the Butterfly Mansion. Luckily, all the nearby people were injured and too deeply asleep to care tonight. Aoi gasped as she took in who had frightened her by appearing suddenly in her path.

“Nezuko-san!” She sighed. “Please don’t scare me like that… I thought you were the ghost that everyone’s been talking about lately."

Nezuko tilted her head and gave Aoi a questioning look. It was cute. Aoi felt her jumping heart calming at the sight.

Nezuko grasped Aoi’s sleeve and tugged it. Aoi blinked. “Nezuko-san? Do you need something?”

Aoi followed Nezuko as she headed down the hallway. After a few turns, they came across an interesting sight.

Someone was dragging a corpse across the floor.

Aoi had been ready to scream, but she didn't because she recognized who the person and corpse were. It was Kuwajima-san dragging a sleeping Zenitsu across the floor. Zenitsu was as limp as a noodle and snoring obnoxiously.

“Kuwajima-san? Do you need help with him?”

The old man shook his head. “No, you should head to bed. It’s late, and I’m used to taking him back to bed now.

Aoi stared at the two. “This has happened before?”

The ex-Hashira nodded. “This isn’t the first time Zenitsu has sleepwalked to find me.”

Aoi’s eyes widened. “What? How long has he been doing that? He’s still injured! He shouldn’t be walking.”

Kuwajima quietly chuckled. “He’s a stubborn brat. He’s been doing it even before he woke up from the run.”

Aoi was shocked. “Really?” Then, something hit her. “Is that why you were so insistent on sleeping at his side?”

Jigoro nodded. “He doesn’t sleepwalk if I’m next to him.” The old man sighed. “I started sleeping in a separate room because I thought he’d stop doing it after he woke up and found out I was fine, but he still comes sometimes.”

“He manages to find you every time?”

“Zenitsu has a keen sense of hearing that allows him to navigate while asleep,” Jigoro explained.

Aoi frowned. “Why didn’t you tell anyone about this? This can’t be good for his injuries.”

Jigoro grimaced. “I assumed that he would struggle against any restraints and cause a ruckus at night. They’d probably upset him and his injuries too.”

Aoi looked down at the sleeping slayer. “I can see that. We should tell the others though. They can probably figure out something to stop him.”

Jigoro reluctantly agreed, and the trio continued down the hallway with Zenitsu’s deadweight. It was peaceful until Aoi snapped her head around to look at the cultivator and his disciple.

She exclaimed, “Wait, he’s been going around the hallways at night! He’s the ghost everyone’s been talking about lately?”

Jigoro coughed. “Zenitsu usually reaches my room, but I’ve caught him shuffling in the hallway calling for me. I can understand why they’d think he was a ghost.”

The cultivator sighed. “He sounds hellish when he’s groaning from his injuries.”

Aoi facepalmed. Nezuko patted her sympathetically.


Later that morning


Zenitsu was surprised when Shinobu entered. He was almost recovered, so her visits had become infrequent.

“Zenitsu-kun, good morning!” Shinobu beamed at him.

“Good morning,” he eagerly replied. Seeing a beautiful woman so early in the day was a sign of good things to come! “Why are you here, Shinobu-san?”

She continued to smile as she sat down next to Zenitsu. She was also smiling when she tied his arms to the bed.

“Eh? Shinobu-san? Wh- what are you doing?” Zenitsu blushed and stammered. C-could this be the… the legendary b-

“This is just a precaution, Zenitsu-kun!” She added, “For your health, of course.”

Zenitsu was confused. “My…health?”

Shinobu nodded. “You’ve been moving around too much, so your injuries are recovering slower than expected. Hopefully, this will help!”

She also ended with a finishing blow. “It looks like you’ll have to stay in bed longer by a few days too.”

That morning, Zenitsu wailed in despair. A beautiful woman visiting in the early morning had not been a good sign.

Still, Jigoro would have gotten Shinobu to tie up Zenitsu earlier had he known that Zenitsu, even unconsciously, would not struggle against a restraint placed upon him by a beautiful lady. The restraints worked, and everyone had the chance to sleep well at night. The rumors faded away over time. It was a happy ending for everyone.


4. Bonk! Go to horny jail, Zenitsu!


Tanjiro and Inosuke had visited him when he was on bed rest. They had seemed relieved and happy that he would be coming out with no permanent injuries. Inosuke had even refrained from challenging him to fights, but Zenitsu knew the slayer would start again the moment he recovered.

This was why Zenitsu was completely blindsided by Tanjiro’s headbutt of doom. Zenitsu had not expected Tanjiro of all people to be the first one to initiate violence on him. He thought his friends would’ve been happy to see that he had finally recovered completely, but Tanjiro had immediately pounced. Man, his friend really had a hard forehead. It hurt! It hurt so much!

Zenitsu was left crouching while clutching his head. He aimed a wet glare at Tanjiro and wailed, “Why’d you do that? What was that for, Tanjiroooooooo!”

To add insult to injury, Inosuke began to gleefully bonk Zenitsu on the head. Zenitsu was torn between swatting at Inosuke, the bastard, and defending his poor, aching head. He deserved a break, dammit! He’d just finished his bed rest and rehab!

Inosuke grinned broadly as he chanted, “Bonks for Zeninsu! Bonks for Zenatsu! Bonks fo—”

Zenitsu roared as he angrily charged at the boar-masked fiend, but Tanjiro, damn him, got in between them.

The weirdo brightly smiled at the blonde as he answered Zenitsu’s earlier question. “Because you deserved it!”

Zenitsu gaped. He was snapped out of his fugue by Inosuke bonking him once more. Zenitsu angrily snapped, “Stop it, dumbass!”

Inosuke laughed. Tanjiro laughed as well.

Zenitsu was so done. He wanted a refund. Why were these idiots his friends? Somehow, what Tanjiro said next partially answered Zenitsu’s thoughts.

“You worried everyone, Zenitsu.” Tanjiro softly said. He had stopped laughing upon seeing Zenitsu had truly had enough and was about to erupt.

“That day,” Tanjiro hesitated before exploding. “You left without warning! You completely disappeared after acting all wrong; how could we not worry about you?”

Inosuke, who had stopped celebrating his successful bonking, added, “We didn’t know why you were acting weirder than usual.” He nodded solemnly. “You were so fast we couldn’t see you.”

Tanjiro still sounded frustrated. “Yeah! We couldn’t do anything! You were just gone. We had to find out from Shinobu-san what happened. And then we sat through an entire Hashira meeting before anyone explained where you were.” He crossed his arms and pouted.

Zenitsu tried to speak, but Tanjiro steamrolled over him. “And! When you came back, you were so injured! You looked horrible, Zenitsu!”

Inosuke smirked. “And you didn’t even fight any demons! You did all that to yourself!”

Tanjiro agreed with Inosuke. “You shouldn’t have pushed yourself like that and injured yourself, Zenitsu. We were all worried that you wouldn’t wake up.”

That dampened the mood. The trio stood there awkwardly for a moment before Zenitsu spoke up. “I had no choice.” Zenitsu met their eyes. “If I hadn’t pushed myself, I could’ve lost Gramps. There was no way I’d let that happen.”

Zenitsu could see that the two understood, but they still had things to say. 

“You didn’t have to run there!” Inosuke waved his hands around.

Tanjiro added, “You could’ve talked to someone at HQ to confirm it first. Maybe they could’ve sent Uzui-san or someone else fast.” He frowned. “In the Hashira meeting, we had to explain where you were, and someone thought you might’ve defected with the way you disappeared on us.”

Tanjiro continued. “You could’ve had Chuntaro send a message to Kuwajima-san before you visited him. You didn’t have to run all the way there by yourself.”

Zenitsu scowled. “Fine, I panicked, but what if someone had already told Gramps? If he knew about Kaigaku before us, I might’ve been too late even if I had left immediately.”

Everyone winced at the thought.

Zenitsu muttered, “Besides, he probably wouldn’t have listened to a letter. He’s stubborn like that. Kept dragging me to training even after I ran away so many times…”

“So, yeah! I don’t regret running there! Even if it did hurt...” Zenitsu began to sniff wetly after remembering the horrible pain from the run and how the blade had looked as it approached Kuwajima.

Tanjiro softened. “Look, Zenitsu. We’re just saying that you shouldn’t neglect yourself like that.” He looked down. “And… I’m sorry we weren’t there for you. You normally cling to us when you're scared, but this time... we couldn’t even follow you when you really needed it.”

Inosuke thumped his chest. “The great Inosuke takes care of his minions!” He pointed at Zenitsu. “Minions shouldn’t ditch their boss!”

Tanjiro laughed. “What Inosuke said.” He gently smiled. “We’re your friends, Zenitsu. You should rely on us more when it matters.” He patted a now-weeping Zenitsu on the head.

“If you’re going to run off, at least take us with you!”

Notes:

Zenitsu doesn't remember most of Extras 1, 2, and 3, haha. Wonder if he'll ever find out. :P

Next chapter's extras are more serious and relevant to the story, but I hoped you enjoyed the silly extras! The chapter after that will start the showdown.

Note that the first village is closer to HQ, so the villagers are more aware of demons, while the second village is farther and less aware. Densuke still didn't know enough to differentiate kakushi (the masked ones he mentioned) from slayers though.
Also, note that the letter mentioned in the 2nd extra said "fields." Zenitsu demolished more than poor Densuke's field lol. Out of all the fields, his was the extra because he happened to have a nephew capable of seeing Zenitsu run at full speed. I don't think the average non-slayer could see much more than a blur/light lol.
iirc, Zenitsu cracked the ground when he ran/attacked in the final battle, so that made me think about whether the ground between HQ and Jigoro's house survived. Some of it did, but some did not, as you can see in the extras XD
Poor Zenitsu... couldn't even rest while unconscious. He kept seeking his Gramps at night. He really wanted to find his Gramps :<
This isn't the last time we're going to see Tanjiro and Inosuke! It'd be a shame to ignore their awesome friendship.

I hope I wrote the OCs okay? Let me know what you think! I don't really write OC content and this is the last you'll ever see of them, but I thought some Outsider POV on Zenitsu's run would be hilarious. Let's just say the corps had some trouble cleaning up after Zenitsu, but Kagaya smoothed it over. XD

I wonder if someone noticed the references in the chapter.

Chapter 7: E

Summary:

1. The letter Kuwajima received from HQ in Chapter 3.
2. Jigoro watches Zenitsu train, but he thinks about Kaigaku. Set during Zenitsu's training timeskip.
3. Kaigaku eats a peach. Set shortly after Zenitsu's conversation with Kuwajima in Chapter 5.
4. The letter? hate-mail? Zenitsu wrote shortly after his conversation with Kuwajima in Chapter 5.

Notes:

Again, E is for extras! Next chapter will be the start of the showdown. Thank you for waiting patiently!

I'm also apologizing in advance to Kaigaku fans (apologists? Does Kaigaku have apologists?). Dude's an interesting character (why is he lowkey relatable), and I'm not bashing him... but you understand how Zenitsu and Jigoro are feeling, right? *twiddles fingers

Posted 1/12/2024

(See the end of the chapter for more notes.)

Chapter Text


1. HQ's Letter to Kuwajima


Kuwajima-san,

This letter bears unfortunate news, so please brace yourself. Your disciple, Kaigaku, has defected from the Demon Slayer Corps. Moments ago, a Kasugai crow reported that he accepted Upper Moon 1’s offer and became a demon to save his life.

Upon hearing of Kaigaku’s defection, Agatsuma Zenitsu abandoned Hashira Training. We believe that he is running to your location at extremely high speeds. Based on his progress, it is likely that he will arrive late at night or early in the morning. It would be wise to delay your actions concerning Kaigaku because Agatsuma will likely need medical attention. The Insect Hashira believes that the run will severely burden his body. Please prepare medical treatment for him and contact a doctor in case. After he stabilizes, bring Agatsuma to the Butterfly Mansion for further treatment.

Regarding Kaigaku, defecting from the corps has severe consequences for the traitor and their master. According to tradition, you must commit seppuku to atone. Oyakata-sama, however, bids you to consider living and atoning in a different way. He states that, while death can have meaning, your life would be more useful to the corps at this crucial time. After Agatsuma recovers, please head to HQ and serve as an assistant in the ongoing Hashira training. Atone through the achievements of the others you have trained. According to Oyakata-sama, one bad apple may spoil an entire barrel, but one disloyal disciple does not ruin the rest. We are looking forward to Agatsuma’s future feats and still value your ability to train strong slayers.


2. A Regretful Master's POV


Jigoro watched from a distance as Zenitsu slashed at a training dummy. His boy had come so far. That last blow had been so fast he’d barely seen it. It would have definitely been lethal for a demon. Its head would have flown off immediately. The dummy’s head had landed far from the rest of its body.

The old man winced. For a moment, he had seen Kaigaku in place of the decapitated dummy. After all, Kaigaku, the one who had betrayed his master and the corps to become a demon, would soon find himself at the end of Zenitsu’s blade. Zenitsu was single-mindedly training to slay his former senior brother.

Jigoro figured that Zenitsu himself was probably imagining Kaigaku as he hacked and slashed. It would explain his ferocity and the ruthless cuts inflicted on the dummies. With the way Zenitsu was acting, Kaigaku’s death would not be a painless one. He certainly deserved it.

The cultivator angrily cursed his former disciple for his foolish choices. Kaigaku, that damned coward, had betrayed everyone who had ever cared for him. A former Hashira had personally instructed him in breathing techniques and taken him as a disciple, but the foolish ingrate had tossed it all away the moment he met a demon he couldn’t defeat. Bah! It wasn’t wrong that Kaigaku would soon receive harsh retribution.

Jigoro breathed heavily due to his anger, but it dissipated when he was forced to dodge a projectile. Zenitsu had decapitated another dummy whose head had flown hard and fast enough to nearly take off his master’s head. Impressive considering Jigoro had made sure to sit far out of the danger zone.

The boy had been training for hours now. It was late, so Jigoro shooed the slayer off to rest and began cleaning up the training field. The blonde had protested and even tried to help clean up, but Jigoro had whacked him, reminding the youth of his aching and overworked body. After that, Zenitsu had folded literally and figuratively.

Jigoro smiled fondly. He was grateful and proud of Zenitsu for training so hard to reclaim his master’s honor. He had full confidence in Zenitsu’s victory.

Still, Jigoro hated how conflicted he felt about that. He rationalized that Kaigaku deserved death and that the demon’s unsightly end would be a consequence of his actions, but the ex-Hashira knew it wasn’t so simple. He had been Kaigaku’s master, the one who should’ve raised him into a brilliant Hashira. To put it simply, he had failed and consequently been betrayed.

Had he been blinded by Kaigaku’s talent with the sword? He knew Kaigaku’s swordsmanship was nearly excellent enough to reach the level of a Hashira. The first form eluding him had been the reason Jigoro hadn’t easily declared Kaigaku his Tsuguko. The first form was the foundation for the rest, and Jigoro knew that Kaigaku would not truly be a master of Thunder Breathing without it.

Kaigaku had always been sensitive about Jigoro refusing to name him as his only Tsuguko. The cultivator also remembered Kaigaku’s reaction to Zenitsu’s arrival. Kaigaku had always been wary of Zenitsu ousting him. Maybe Kaigaku’s betrayal had been festering within him even before he became a slayer.

Jigoro had truly intended to treat his disciples equally, but perhaps Kaigaku perceived favoritism toward Zenitsu. Jigoro’s relationship with Kaigaku had differed from the ex-Hashira’s relationship with Zenitsu. Kaigaku had treated him as more of a master, while Zenitsu had never stopped calling him Gramps. Due to that, Jigoro had naturally treated them slightly differently although he didn’t prioritize one over the other. Had he failed to do that though? Perhaps he’d never know given how Kaigaku was going to be decapitated soon.

For all his grief and anger, Jigoro couldn’t place all the blame on his former disciple. Kaigaku’s defection signaled that he was a cowardly weakling who should have never been considered for the position of Tsuguko, but Jigoro had been the one to pick and train him. He had believed him ready and sent him to the Final Selection.

The cultivator’s choices had led to Kaigaku’s demise. Faced with Upper Moon 1, Kaigaku’s choices had been to die or defect. As a cultivator, Jigoro knew that he would’ve wanted Kaigaku to stand strong like the Flame Hashira had, but as a grandfather...

Jigoro sighed. It didn’t matter. From the moment he met Upper Moon 1, Kaigaku was fated to die. Even if Jigoro had been a better master or acted more like a grandpa for him, Kaigaku would have ended up dead. Zenitsu had survived his Upper Moon confrontations while Kaigaku hadn’t.

If only Kaigaku hadn’t met Upper Moon 1.

Still, Jigoro couldn’t help but feel that Kaigaku’s death at Upper Moon 1 would have been more peaceful for everyone. His impending death had led and would lead to more anguish. The defection of a strong slayer had damaged the corps’ morale, and it would be physically and mentally difficult for Zenitsu to kill him. Lastly…

Dying under Zenitsu’s blade would definitely be one of Kaigaku’s least preferred ways to go, Jigoro thought wryly.


3. The Trash's POV


Kaigaku stood in front of his master’s— no, ex-master’s house. Now, he only served Kibutsuji-sama and Kokushibo-sama. Er, he’d probably follow the orders of the other Upper Moons as well but that wasn’t important right now.

He had been tasked with bringing his former master’s head as a test of his loyalty and strength. Retired or not, aged or not, Kuwajima had been a strong Hashira and was sure to put up a fight… had he been present.

The house was clearly abandoned. Heck, even the front wall had been obliterated. Kaigaku strode forth and entered the building. The rubble hadn’t been cleared, but Kuwajima’s possessions had been mostly removed.

Glancing at the mat and wooden block on the floor, Kaigaku wasn’t sure if Kuwajima lived or not. There were no bloodstains, at least not here. Nothing stood out to him except for the scrap of paper stuck to the wooden block. It had his name on it.

Kaigaku picked it up and read it. He grinned sharply before tearing it to shreds. Kaigaku had thought his mission would be a failure, but it looked like it would merely take longer. As a demon, he had time. He would prove that he deserved the position of Upper Moon 6.

The demon left. On the way out, he impulsively picked up a peach that had fallen from its tree. Out of habit, he bit into its juicy flesh. Kaigaku swallowed and regretted it.


4. Zenitsu’s Letter to the Trash (Delivered by Chuntaro)


“Kaigaku, you bastard, I’ll kill you a year from now. On XXXXX, I’ll slice your head off here, and you’ll take Gramps’ place in the afterlife. Wait for it, scum.”

Notes:

If it wasn't clear, Extra 4 was the scrap of paper Kaigaku read in Extra 3.
As stated earlier, Jigoro finished reading the letter (its third paragraph) while Zenitsu was unconscious. Dude still really wanted to commit seppuku though. Zenitsu's conversation with him in Chapter 5 was actually what made him reconsider. It all hinges on Zenitsu now!

Sorry about the chapter having like no dialogue. In my defense, we'll get to the action next chapter?
Also, the Jigoro section was inspired by a comment from Vasrod95. Thank you!

Some help please! Could someone explain this piece of trivia from the wiki? Kaigaku got a kimono from Jigoro (identical to his own), but Kaigaku never wore it. I skimmed Volume 17 (it was cited as coming from there), but I couldn't find anything about it. Is this accurate?

EDIT: Churned out most of Chapter 8 in one go just now... It's a longer one (ouph, editing is gonna be slow...)! Everyone's comments really motivated me tonight. Big thanks!

Chapter 8: D

Summary:

The showdown begins.

Notes:

Thanks for the 100+ kudos and 1k+ hits! First time I’ve gotten into the triple-digits and thousands. Sorry about the longer author’s note at the bottom, but I’m probably almost as excited about this chapter as you are, haha.

Also, I just assumed that Kaigaku’s strength was around canon. This fic’s timeline is canon divergent (couldn’t find details about the canon timeline, so I gave up lol) because Hashira Training might’ve been longer & Zenitsu was unconscious for a while after the run. Still, this took place before Infinity Castle, so Kaigaku wouldn’t be that different from canon. Maybe a little stronger. We’ll see if that matters. ;)

Posted 1/19/2024

(See the end of the chapter for more notes.)

Chapter Text

It was nearing the date that Zenitsu had angrily scribbled and left for Kaigaku.

Zenitsu had become stronger. He could feel it, but a successful slew of missions had also corroborated it. Zenitsu still shook in fear when slaying demons, but he could do it when awake. Besides, Zenitsu knew he wouldn’t be feeling fear when he faced Kaigaku. No, he would be enraged. Furious. He’d slice that bastard’s head off instantly.

Jigoro was proud of Zenitsu as always, but he also mourned how this growth had occurred as a result of Kaigaku’s defection and Jigoro’s failure.

Tanjiro and Inosuke, however, were concerned. Sure, they were impressed with Zenitsu’s new prowess and lack of crying or whining, but Zenitsu had become grimmer after he woke up from his run. He still smiled at them and the Butterfly Girls, but he no longer went around shouting “Nezuko-chaaaaaaaaaaaaaan” or bothering the girls with his flirting attempts. He had cheered up a little after he trained with the former Sound Hashira, but Zenitsu had still changed.

He was more serious and determined despite his cowardly side still showing up from time to time. On the few joint missions they had taken post-change, Zenitsu had started shaking the moment he detected the demon with his keen hearing, but he had ruthlessly decapitated it once he finally saw it. Previously, he would’ve hung back and let Inosuke and Tanjiro charge forward. In the past, he would’ve also needed to fall unconscious or asleep to defeat a demon.

These changes boded well for his chances at slaying Kaigaku, but Kaigaku was surely stronger than the run-of-the-mill demons they had recently slayed for training. Tanjiro vividly remembered their Upper Moon confrontations. He hoped Zenitsu’s fight would go easier than those times.

Tanjiro promised himself that he would be more useful this time. He and Inosuke would force Zenitsu to let them accompany him to the fight. If needed, they would ensure that Zenitsu would live regardless of his or Jigoro’s honor.



“Oi, Zenitsu! You said you’d let us come with you!” Tanjiro called as he and Inosuke ran after Zenitsu.

Zenitsu turned his head to look at them. “You made me promise that!” He angrily shouted.

“You still promised!” Inosuke shouted, bouncing along.

“Yeah, and I’m letting you follow me, aren’t I?” Zenitsu retorted.

“Slow down then!” Tanjiro huffed. “We can’t keep this pace the entire time, and you need to save your energy for the fight!”

Zenitsu huffed but still slowed down a little.

“Also!” Tanjiro sprinted to run alongside Zenitsu. “You left without warning! Why didn’t you say goodbye to anyone? Kuwajima-san is going to be worried!”

Zenitsu replied, “Knowing I was leaving to fight that bastard would’ve made them worry too. Besides,” he casually added, “I don’t need to say goodbye because we’ll be back soon anyways.”

Inosuke jumped in. “Wow, Zenisu actually sounds strong for once!”

Zenitsu snapped at Inosuke. “Shut up!”

Tanjiro laughed at their antics. “Yeah, you’ll kick his ass in a flash, and we’ll be back in time for dinner!” He joked.

Zenitsu snapped his head around to look at Tanjiro. “Not you too! Shut up!” The angry blonde sped up once more.

“Hey, slow down!”

No one, not even a bird in the sky, slowed down.



The trio made good progress and soon neared the site of the showdown. They had been traveling at a comfortable speed compared to Zenitsu’s previous marathon, so the three of them weren’t overly exhausted. They’d slowed to a walk as they approached Kuwajima’s residence. The closer they got, the more nervous Zenitsu grew.

“Do you think he’s there yet?” Zenitsu asked. He told himself he was ready to defeat Kaigaku, but he definitely didn’t feel ready right now. His legs felt weak, and if they hadn’t been running at the moment, Zenitsu was sure they’d be trembling.

Tanjiro noticed Zenitsu’s sweaty and pale face, so he reassured Zenitsu that Kaigaku probably hadn’t arrived yet since it was still bright out. After all, wily demons wouldn’t announce themselves or give away their location during the day since they’d be restricted by the sun in a fight.

Inosuke agreed and added, “No way we’d miss him.” Inosuke couldn’t sense any demons in the area, and he figured that Zekatsu and Tonjuro would be able to respectively hear and smell if any approached.

The boar-masked slayer suddenly waved his blades around and shouted, “Don’t sweat it, Chuitsu! The great Inosuke will kill anyone who approaches!”

Zenitsu backed away and sweatdropped. “You mean any demons besides Kaigaku, right?”

Tanjiro laughed. “Yeah, we’ll stop anyone from interfering with the fight. You can focus on what you came for, Zenitsu.” He patted the blonde on the shoulder. “We’ve got you this time. You can do it! You’ll win.”

As Zenitsu started blubbering over how unusually nice the two were being, Tanjiro and Inosuke shared a quick glance. When they argued with Zenitsu about whether they could accompany him, Zenitsu had been adamant that the two of them wouldn’t intervene at all in his fight with Kaigaku. The two of them had promised, but they knew they’d intervene if necessary. Even if it was dishonorable, they couldn’t let their friend die in front of them.

Although they predicted that Kaigaku wouldn’t arrive until it was completely dark, the three of them carefully checked the residence and its surroundings once they arrived. There were no recent traces of Kaigaku, but they found that Zenitsu’s letter had been shredded.

The sun hadn’t set yet, so the three of them waited in front of the residence. Zenitsu was full of nervous energy and on the way to becoming a nervous wreck, so Inosuke and Tanjiro had their hands full calming him down. While they waited, they also ensured Zenitsu would have enough light to fight by.

About an hour after darkness settled in, the three of them stilled. Zenitsu could hear footsteps approaching rapidly, and Inosuke could feel the heavy pounding coming from afar. Tanjiro hadn’t smelled anything yet likely due to the wind’s direction, but he gripped his blade once he noticed the others’ reactions. It wasn’t long before he smelled the scent of a demon, a strong one.

“Zenitsu…” he began, turning to look at his friend. Tanjiro was worried because Zenitsu was still looking a bit peaky even after all their reassurance and encouragement.

Despite his unconfident appearance, Zenitsu straightened up and stepped forward. “He’s here.”

And he was. The three of them watched as Kaigaku strode toward them. His footsteps had slowed as he neared the four.

Despite the dimness, Zenitsu took in his former senior’s new appearance. Kaigaku’s skin had paled, and he had gained black markings on his face. Zenitsu was somewhat relieved that Kaigaku seemed humanoid still, but he also felt that Kaigaku deserved to turn into a hideous monstrosity after what the traitor had done.

Zenitsu had expected to see fangs and unusual eyes, but his heart shook as he recognized the kanji etched in Kaigaku’s eyes.

Upper Rank 6.

Kaigaku, that bastard… he’d really done it. Zenitsu had hoped that Kaigaku would adapt poorly to being a demon, but it seemed as if Kaigaku had flourished instead. How many humans had Kaigaku eaten to achieve that rank? Zenitsu shivered.

Kaigaku smirked, noticing that Zenitsu appeared as pathetic as always. Seemed like he’d have an easy victory. The three of them together wouldn’t be strong enough to threaten him. After all, he was Upper Moon 6. They weren’t Hashira, just a trio of weaklings. Zenitsu’s two groupies would also serve as a nice celebratory snack once he was done with the blonde.

Mind made up, Kaigaku sneered and spoke, “Cat got your tongue, Zenitsu? I thought you might’ve grown a backbone after challenging me, but you haven’t changed at all. Look at how pathetic you are, shaking like that. Puny and weak as ever.”

Tanjiro grew indignant but kept quiet. Zenitsu’s back was still straight even though he was shaking and hadn’t responded to Kaigaku’s mocking.

 Zenitsu took a deep breath, and his eyes sharpened. “You’re wrong.”

“Oh?” Kaigaku raised an eyebrow.

“Now that you’re a demon, you have no right to call me weak,” Zenitsu calmly stated. His voice was steady despite his shaky limbs.

“Tch. You’re certainly no Hashira. Meanwhile, I’ve become strong.” Kaigaku snickered before he mockingly asked, “Have you learned anything besides the first form yet?”

“Have you learned the first form yet?” Zenitsu shot back. “You were never going to become a Hashira. Gramps was right to not make you his sole Tsuguko.”

Zenitsu spat on the floor. “Look at you now, playing stopgap as the weakest Upper Moon. That was all it took to satisfy you?”

Kaigaku briefly froze, noticing the cold glint in Zenitsu’s eyes, but a menacing smile soon slowly stretched across his demonic face. The demon barked out a laugh before he said, “I’m the seventh strongest demon in existence. After tonight, you’ll never become a Hashira. You’ll forever remain a weakling, a no-name slayer…”

The demon drew his sword. “Because you’ll be dead.”

Zenitsu ignored the threat and stared into the demon’s kanji-marked eyes. The slayer coolly stated, “You were dead the moment you willingly became a demon. So…”

“Why did you become a demon? Why’d you betray us?”

Kaigaku opened his mouth, but Zenitsu cut him off. “Did you ever think about what your betrayal meant for Gramps?”

Zenitsu’s glare pierced Kaigaku, but the demon scoffed and callously said, “No, why would I? I don’t care about the old fart.”

The former slayer smirked. “But I did see his seppuku preparations. Did he go through with it? He deserved it for making me share the successorship with a weakling like you.”

Zenitsu saw red, and his grip on his sword tightened further. “Gramps is alive. And he’ll live way longer than you, scumbag. You’re the one that deserves death.”

Kaigaku shrugged. “It’s a shame he didn’t die. He was a fool that didn’t understand sharing isn’t caring.”

In the background, Inosuke blurted, “I thought it was ‘sharing is caring,’” only to be shushed by Tanjiro. Luckily, the two Thunder Breathers were too absorbed in their confrontation to notice.

Zenitsu growled, “Gramps isn’t a fool.”

“Gramps was the Roaring Hashira, one of the strongest slayers. He was just unlucky enough to have two disciples who couldn’t master Thunder Breathing. Now, he only has one.”

The demon slayer sneered. “You claim you’ve gotten stronger, but you haven’t even learned the first form yet, haven’t you? You still don’t know the basics.”

Zenitsu jabbed his finger forward. “I may be the weakling that only knows one form, but you’re not even human. You’re worse than dirt!”

Zenitsu’s voice had become louder and more intense as he spoke, but Kaigaku’s response was shouted as if he could drown out the truth by speaking louder.

“Shut up! I’m special unlike you! You’re nothing compared to me!”

Enraged, Kaigaku unleashed a ranged attack, releasing the fourth form of Thunder Breathing at the trio. Tanjiro and Inosuke leaped backward, distancing themselves now that the fight had begun.

Zenitsu dodged Kaigaku’s attack, hand remaining over his sword’s hilt. Kaigaku kept up a constant flurry of attacks, but Zenitsu avoided them all.

Kaigaku was astounded by Zenitsu’s speed. Although Zenitsu hadn’t attacked yet, his speed was insane. His movements felt completely different from the past. For less than a second, Kaigaku was worried that Zenitsu actually posed a threat to him.

But then he remembered Kokushibo-sama. Kaigaku had never experienced true fear before meeting him. That fateful day, Kaigaku had literally tasted death. He’d had no choice but to bow before Upper Moon 1’s overwhelming might. Zenitsu, however nimble and irritating, was absolutely nothing compared to Kokushibo-sama.

Amid his slashes, Kaigaku mocked Zenitsu. “You talked big, but you haven’t even unsheathed your sword! You’re too busy fleeing like the coward you are!”

Suddenly, Zenitsu was in front of him. Kaigaku’s eyes widened as he saw Zenitsu’s eyes fly open. The demon belatedly realized they’d been closed until now. Something was wrong. He frantically moved, but…

The next thing he saw was blood. His own blood, fresh from his neck, sprayed into the air. He hadn’t even felt the attack, but he remembered what Zenitsu had whispered into his ear as the slayer passed by.

“Too slow, trash.”


Moments before first blood


Tanjiro, Inosuke, and Nezuko spectated from the side. Most of the boys’ attention was on the surroundings since they had promised to ensure the fight wouldn’t be interrupted or interfered with.

Still, they could see how awe-inspiring the fight in front of them was. Despite their own skill, they were having difficulty even seeing the two Thunder Breathers move. Kaigaku’s black lightning flew everywhere, but the golden blur that was Zenitsu remained untouched.

Tanjiro remembered meeting Zenitsu for the first time. His friend had come a long way from that sobbing, desperate simp who had been harassing a young lady.

Inosuke was impressed that Zenitsu was evenly matched with an Upper Moon. He saw that this Upper Moon wasn’t as strong as the previous Upper Moon 6 and definitely nowhere near Upper Moon 3, but Zenitsu was finally proving he was a minion worthy of the great Inosuke. After seeing such an intense fight, Inosuke was itching for some action as well.

Suddenly, the boar-masked slayer looked upward. Tanjiro, following Inosuke’s movement, also noticed that the nearby trees were occupied. Inosuke’s grip on his swords tightened. He would protect Zenitsu from any ambushes, not that it seemed necessary now. The fight was almost over.

Everyone proudly watched as Zenitsu blitzed past Kaigaku.


Immediately after first blood


Kaigaku gaped as he clutched his wounded neck. “How?”

Before Zenitsu could even decide if he wanted to answer, the demon snarled, “A lucky hit, huh. You won’t get a second chance, dirt.”

This time, Zenitsu watched as his former senior launched a plethora of attacks at him. His eyes were open as the second form, third form, and fifth form came for him once more.

Although Zenitsu never learned to use these forms, Gramps had had his disciples spar with each other, so Zenitsu was already somewhat familiar with the forms and Kaigaku’s movements despite his many losses. This time was going to be different.

Zenitsu dodged all of Kaigaku’s Thunder Breathing forms almost effortlessly. By now, they all sounded familiar. He begrudgingly thanked Uzui in his mind. Looked like training with that weirdo had been worth it after all. He hadn’t made the wrong decision that day.


During Zenitsu's training


Zenitsu flopped on the floor during a break in Uzui’s Hashira Training. The youth yawned. Gramps had been on his case lately. He hadn’t been able to sneak out for nighttime training, so he had actually slept well last night. That was only making him feel more tired though. Zenitsu had decided to briefly rest his eyes during break. He had just closed them, but.... What was that weird feeling?

He opened his eyes to see Uzui’s eye drilling holes into him. Zenitsu yelped.

“What are you looking at me like that for?” Zenitsu snapped at the ex-Hashira.

“How good is your hearing?” Uzui asked.

Zenitsu is confused. “What?”

Uzui huffed. “Your master told me that you have extremely sensitive hearing. We talked, and I asked him how the heck you were running while asleep during training.”

Zenitsu blushed. “Ah, I have good ears, I guess.”

Uzui rolled his eye. “Yeah, we’ve confirmed that, punk. How strong is your hearing exactly? Can you hear that bird in the distance?”

Zenitsu’s eyes widened. “You can hear it too?”

The former Sound Hashira rolled his shoulders. “Yeah, I have the ears of a god. Let’s compare. Maybe even someone like you can learn some tricks from a god like me.”

Zenitsu complained, “Hey, wait! What do you mean by ‘someone like me?'” but followed the man anyway. Screw his pride; he had to get stronger even if it meant learning from someone as weird as Uzui.


The present


Zenitsu had never learned the Thunder Breathing forms Kaigaku mastered, but he could learn how Kaigaku used those forms. Thanks to the Sound Breather's guidance, all of Kaigaku’s movements were now transparent. Training with Uzui, previously the fastest Hashira alive, also helped Zenitsu adapt to his former senior’s increased speed and strength. The former Hashira had slayed the previous Upper Moon 6 after all.

In their training sessions, Uzui had explained his Musical Score technique. Although Zenitsu couldn’t literally convert his enemies’ attacks into sheet music, the younger slayer had trained with the ex-Sound Hashira to be able to recognize and preempt enemy attacks. It had taken weeks before Zenitsu had been able to preempt some of Uzui’s attacks, and the one-armed bastard had mercilessly smacked him black and blue by then.

The pain and humiliation had been worth it though.

Zenitsu had always been able to pick up people’s thoughts, emotions, and personalities through his enhanced hearing. Uzui’s training sessions inspired him to apply that to combat. Although Zenitsu had initially only been able to recognize that certain sounds indicated an incoming attack aimed at a specific body part, he eventually started hearing the intent behind each attack.

After all that training, all Zenitsu had needed to do was close his eyes and focus for a few moments before he could hear and identify the intent preceding each movement the traitor made. He didn’t have anything as flashy as an entire musical score, but Kaigaku had become entirely predictable.

For all his demon-enhanced skill, strength, and breathing forms, Kaigaku wouldn’t be able to reach Zenitsu ever again.

Notes:

I wrote half of Kaigaku’s dialogue without reading the manga, so I was astounded to see that I was really close to the kinds of things he said in canon.

RIP Kaigaku though. Bro hasn’t even landed a single blow, so the special cracking effect he’s probably proud of hasn’t been revealed. This fic is not tagged as Kaigaku-centric for a reason :P Sorry, dude. I just couldn’t figure out how to get you to land a hit on GS's BAMF Zenitsu…
Also, I think Kaigaku showed up as early as he could because he wanted as much night as possible (Akaza showed why being late to the party isn’t fun). This says something about how he truly feels, hehe.
Sharing isn’t caring (according to Kaigaku). Had to include that even if it was a bit silly.

This isn’t the last you’ll see of Tengen! He paid more attention to GS! Zenitsu than canon! Zenitsu, so Zenitsu goes untouched this time. He sparred with Uzui who’s hella fast and strong, so GS! Zenitsu’s speed and dodging skills are superior to canon Zenitsu who probably mostly trained on his own. I like to think that GS! Zenitsu was even more motivated because he had something to lose (Gramps’ life) unlike canon! Zenitsu.

Let me know if the sequence of events gets confusing anywhere in the fic! I jumped a bit in this chapter (and the next). I’ll clarify and perhaps edit if needed. Also, Tanjiro & Inosuke asking to go with Zenitsu happened off-screen, probably after Chapter 6's last extra.

Also, has the fight been epic enough for you so far? It’s my first complicated fight scene. Didn’t want to stick to canon exactly, but it’s such a good fight (can’t wait for it to be animated!) I couldn’t help but include some aspects of it. No way I was leaving out Zenitsu's iconic line.

Hashira Training Arc trailer released whooooo

EDIT: Dayum, next chapter's probably gonna be the longest. It's almost 3k, and it's not even done yet. Save me XD

Chapter 9: ,

Summary:

The showdown ends.

Notes:

I have some questions for you all at the end! A survey of sorts. Please check it out! I'd appreciate it. ^_^

I didn’t really give you all a cliffhanger last chapter, but I felt that making you wait in the middle of a final showdown was :/ so here you go! Enjoy! We're almost at the end, huh.

Posted 1/21/2024

(See the end of the chapter for more notes.)

Chapter Text

Taking one last glance at Kaigaku, Zenitsu muttered, "I wanted to fight alongside you one day.” Sorry, Aniki.

He would never hear Kaigaku’s dissatisfied sound again.

 

 

Thunder Breathing Seventh Form: Flaming Thunder God.

 

 


During Zenitsu's training


“Oi!” Tengen exclaimed. “Stop being so mopey! You’re dragging down the atmosphere and pissing me off!”

Tengen was running stamina training. The training slayers were all speeding along obediently, although they all looked like they wanted to die, except for one who looked like he really wanted to die. It was irritating how gloomy the punk looked. Tch. They should be thanking him for taking time out of his retirement to train them.

Zenitsu glanced at the eccentric man. “What?” He asked flatly as he jogged by.

A vein pulsed on Tengen’s head, and he snatched the kid up by the collar when he next passed by.

“Oi, I’m not your master, but you’re training under me right now! Don’t give me that.”

Agatsuma looked unimpressed. “I haven’t been doing anything.”

Tengen sighed and shook his head. How hopeless. “You’re making your face even uglier with that facial expression you constantly have. With a face like that, you’ve got to do your best, not make it worse.”

He pointed at the gaping blonde. “You look absolutely constipated! It’s terribly unflashy! I can’t bear to see it any longer!” He snapped his fingers at Agatsuma’s face.

“Hey, what’s the matter with you? Why do you always look like you’re about to die? Training’s supposed to prevent that, so focus on it.”

The kid made an even uglier face as he shouted, “Shut up, idiot! Leave me alone!” and stomped off.

There was no way Tengen would leave it at that. First, Agatsuma was ditching training. Second, he was ignoring the God of Flashiness and Festivals. Third, whatever was affecting the boy really was dragging down his training’s atmosphere. He’d had to smack sense into several trainees who were too busy gossiping about the tragedy faced by the Thunder Breathers. Maybe if Agatsuma stopped going around looking like he always smelled something nasty, they’d shut up and actually focus on their stamina training.

As for a fourth reason, there was no fourth reason. Definitely not.

Tengen knew Agatsuma was fast after their fight with Upper Moon 6 and the kid’s epic dash to his master, but it’d be years before he had a chance of beating Tengen’s speed. He easily caught up to the angry youth.

“I’ll leave you alone when you’re faster than me,” the ex-Hashira teased.

Agatsuma merely rolled his eyes and groaned. Tengen twitched. “Punk, don’t treat your superiors like that!” He grabbed Zenitsu’s shoulder (Disgusting. It was sweaty!), and spun the boy around to face him.

“What’s the matter with you? Spit it out.”

“You’re the one bothering me, moron,” Agatsuma replied.

Tengen was seeing red. His grip on Agatsuma’s shoulder briefly tightened before he forced himself to let the boy go.

They stared at each other for a moment. Tengen sighed. “Kid, what’s wrong? Just tell me already.”

Zenitsu was so done. “Ugh, you know what’s wrong!” He shouted. “Everyone knows what happened with that bastard!”

Tengen eyed him. “Is that what’s bothering you? The other trainees? I’ve already shut up a few of the gossips.”

The blonde muttered, “No, that doesn’t bother me.”

Tengen waited, but it looked like Agatsuma wasn’t continuing. The ex-shinobi knew he was getting close though. He could hear that the boy was about to open up about whatever was bothering him.

He tried again. “What, are you afraid?”

Agatsuma straightened up. He indignantly replied, “Huh? I’m not!” but Tengen had heard his heart stutter for a second. Aha.

The white-haired man grinned triumphantly. He leaned forward and smugly taunted, “You sure? My ears don’t lie.”

Zenitsu knew that Tengen had sensed weakness and was attacking it like a predator. Ugh, Inosuke’s wildness was contaminating him if he’d thought that. He gritted his teeth and resolved to give nothing else away.

Zenitsu scowled and tried to turn away, but the bastard was too fast. He easily appeared in front of Zenitsu. It was infuriating.

“You know, you should pay more attention to training if you’re scared.”

“I’m not scared!”

Tengen scoffed. “You’re always scared.”

Zenitsu had no reply.

“Your master’s former disciple must’ve been somewhat strong if his defection caused that much of a fuss at HQ. Stop being so unflashy and focus on getting stronger if you’re scared of losing to him.”

This got a rise out of Zenitsu. “I’m not going to lose to that scumbag!”

Tengen didn’t sense any fear, only indignation and something else mixed in with it that he couldn’t identify. Interesting.

“Yeah? Then why do you look like you’re about to die?”

The youth denied it once more. Tengen was unimpressed. “Punk, we’re not going anywhere until you spill.” He poked the boy’s forehead. “What’s wrong?”

Zenitsu gave up. He was tired, and he really wanted to rest after stupid stamina training. This flamboyant musclehead really wasn’t going to let him go unless he said something.

“He’s a demon and a traitor, but he was my senior brother, okay?” Zenitsu spat out. “Meeting him again like this is going to be weird.”

Tengen was surprised, although he didn’t show it. He was also inwardly cheering at finally getting something of substance from the stubborn brat.

He probed more. “You challenged him to a duel to the death, right?”

Zenitsu muttered, “Yeah.”

“And you’re not afraid you’re going to lose to him?”

Zenitsu crossed his arms. “No, I’m going to win.”

Tengen internally admitted that this confident declaration was flashy, something he didn’t expect from Agatsuma. More importantly, however, his ears had picked up something from the boy’s last utterance.

“Why are you upset about that?”

Zenitsu deflected. “Why would I be upset about winning?”

Tengen stared at him. He could see where this was going. This was not what he had signed up for, but he was the one who had inadvertently volunteered. The man sighed and ran his hand through his hair. “He was your senior brother, and now he’s a demon you’re going to slay.”

Tengen’s next sentence struck Zenitsu hard. “You’re conflicted because you’re about to kill someone who was close to you. You’re afraid of killing him.”

Zenitsu didn’t have anything to say because the ex-shinobi had pinpointed the source of his complicated feelings. It had been easy to declare to the world that he was going to reclaim Gramps’ honor by slaying Kaigaku, but once he’d calmed down, he’d realized what that actually entailed.

Kaigaku had hated Zenitsu, and Zenitsu had reciprocated, but they’d still known each other. Killing Kaigaku was different from killing a random demon. Zenitsu knew that every demon had been a human before, but this was the first time it mattered to him. He’d truly respected Kaigaku and his drive. Kaigaku had been special to Zenitsu. In a way, he still was.

Zenitsu knew slaying Kaigaku would feel different. Sure, Zenitsu was far more motivated to slay Kaigaku than any other demon. He could feel the anger and resentment in him fueling his rapid growth, but something was holding him back as well.

Zenitsu had been silent for a while, so Tengen spoke up. “Hey, it’s normal to feel weird about killing him. I don’t know what your relationship with him was like, but killing someone you know is always hard.”

Zenitsu looked like he was about to protest, so Tengen steamrolled over him. “You’re not weak if you hesitate.”

Zenitsu finally got a word in. He weakly said, “I won’t hesitate.”

Both of them knew that sounded untrue. Zenitsu winced.

Tengen calmly spoke, “Hesitating usually isn’t flamboyant, but…” He paused and looked up. “In this case, it is.”

“Huh?”

Tengen changed the subject. “Don’t let your guilt weigh you down.” He started counting off his fingers.

“You’re feeling guilty because you promised your master that you’d avenge him and reclaim his honor but you’re hesitating because you don’t want to kill someone you knew.”

“You also feel guilty because you know you shouldn’t be hesitating to kill a traitor but you’re still feeling conflicted about it.”

“Lastly, you feel bad about worrying your master and dragging down your friends with your moodiness. You haven’t talked to anyone about your feelings because you don’t want to bother them.”

Tengen tilted his head. “I think that’s it? Got anything else?”

Zenitsu was stunned. The ex-Hashira had fully laid out his feelings.

Tengen shocked him even more when he ruffled the boy’s hair. “You’re wondering how I knew all that, huh?”

“You’re not hard to read, and your friend talked to my friend about your moods.” The ex-Hashira grumbled, “Talked about it too much in fact. My poor ears.”

Zenitsu didn’t really know what to say, so he sat down. The ex-shinobi squatted in front of him and watched him carefully.

“Hey, say something.” The man nudged him.

Zenitsu squinted at him. “Didn’t you say everything already, oh great God of Flashiness?”

Any other time, Tengen would’ve been offended at the heavy sarcasm in the boy’s voice, but this time he took it as a sign that the boy was finally engaging.

He laughed. “It’s okay to admit it. It’s not flashy, but no one expected you to be flashy anyway.”

Zenitsu growled and swatted at the so-called god. The man dodged easily.

He held up his hand. “Hey, use your words, not your stubby little arms!”

Zenitsu flopped back on the ground. “You already know what’s wrong, so go away.”

Tengen joined him and laid down. “Yeah, but you’re still dragging down the mood. Do something about it.”

“Do what about it?”

“I don’t know? Get stronger and work on your flamboyance?”

“Wow, thanks for the useful advice.”

Tengen turned to look at him. “Hey, you’re one of the least flashy slayers I know, but what you’re feeling isn’t wrong and it isn’t weak. Don’t feel bad about it. Just get going.” He nudged the boy again. “Use those speedy legs of yours.”

The boy grumbled and scooted away. He was still clearly in a mood.

Tengen wasn’t getting anywhere. Somehow, the boy’s stubbornness was impressive, but it wasn’t helping. He knew he had to pull out the big guns.

“Your guilt and hesitation aren’t weaknesses.” Zenitsu still didn’t look like he believed him, but hopefully what was next would work. “It’s a strength you have that he doesn’t.”

This got a reaction from Zenitsu, who turned back to look at the man.

“Don’t bother speaking. You’re wondering how the heck are those strengths, right? Shut up and listen.”

Zenitsu thought that offending him wasn’t the best way to get him to listen but listened anyway.

“Demons can murder and eat humans without feeling remorse. They were once human as well, but they’ve long lost their humanity. They’re worse for it.”

Tengen steeled himself. “There are humans who are similar to demons. They… they can kill other humans, even people close to them, without feeling anything.” The ex-shinobi gritted his teeth. “In a way, that makes them worse than demons.”

The two made eye contact. “You’re not like that,” Tengen plainly stated. “Those messy feelings of yours? They’re proof that you’re still human.”

He muttered, “I’d be more concerned if you didn’t feel anything.”

“But!” The man suddenly sat up, giving Zenitsu a scare. “It’s definitely not flashy to let those feelings get in your way! So use those feelings as motivation and slice that traitor’s head off!”

A purple eye pierced Zenitsu. “Accept your feelings and get going! Become as flashy as you can!” Still seated, the ex-Hashira struck a flamboyant pose.

Zenitsu laughed. Tengen looked mildly offended, but Zenitsu couldn’t stop laughing. This was the most ridiculous conversation he’d had in a while. Uzui Tengen, former Hashira and a stud with three gorgeous wives, had followed him into the woods to nag him and give Zenitsu of all people what was essentially a motivational speech. Were all ex-Hashira like this?

“You’re the only one who cares about flashiness.”

“That’s your reply?” Tengen shouted. “After all that, that’s what I get?”

Zenitsu smirked. “I don’t need your words of affirmation to become stronger.” He stood up, and Tengen followed.

“I’ve hesitated enough,” Zenitsu declared. “So, I won’t hesitate when the time comes.” The slayer looked directly at the retired Hashira.

“I’ll be faster than you someday, so you don’t need to worry. Thanks for the motivational speech.” He grinned smugly before he sped off, leaving behind a fuming man.

It had not been a motivational speech, the retired Hashira grumbled in his mind. He wasn’t worried about some punk either. Tengen had been merely dealing with an eyesore. Hopefully, the kid would rapidly improve from now on.

Tengen had noticed that the blonde had been more invested in training after recovering from his run, but the boy had always been held back by his anxieties. He had only known the boy for a little while, but anyone decently strong could tell that Agatsuma had potential. No wonder the former Roaring Hashira had selected him. Tengen looked forward to seeing that untapped potential in action. It would be a spectacularly flashy sight.


A few seconds before present time


They had fought long enough for Zenitsu to familiarize himself with Kaigaku’s attacks, so Zenitsu didn’t hesitate. Surpassing his previously demonstrated speed, he burst forward. The demon slayer put everything he had into his final blow, this singular slash aimed at his former brother’s neck.

 

 

Thunder Breathing Seventh Form: Flaming Thunder God!

 

 

All the spectators were stunned by Zenitsu’s breathtaking attack. Although they couldn’t follow Zenitsu’s movements or his blade, they stared at the magnificent golden dragon his blade had manifested.

It zapped forward and tore Kaigaku’s head off.

Zenitsu, surrounded by the tatters of his treasured yellow haori, impassively watched as Kaigaku’s head soared through the air. It was silent except for Zenitsu’s panting and Kaigaku’s blood splattering on the earthen floor.

Kaigaku couldn’t believe it. He had been ignoring the nonsense Zenitsu was spouting when the world began spinning around him. He hadn’t been able to see Zenitsu’s attack—merely the maw of a lightning dragon. He had only realized what had happened due to how he could see his body from an impossible angle now.

What the heck was that just now? Although Kaigaku couldn’t use the first form, he knew every single form of Thunder Breathing. None of them involved a golden dragon bearing down on the enemy.

He knew he was dying, but at least stupid Zenitsu and his precious geezer wouldn’t live long anyways. The old coot should’ve died instead of Kaigaku. He was already one foot in the grave anyways. Weak slayers always died, and Zenitsu, despite his fancy new form, would always be weak however much he trained. But… if Zenitsu was weak… what about him? He’d fallen under that weakling’s blade. No, Zenitsu had always cheated with how he cozied up to Kuwajima. The old fool had eaten it up and fallen for it, leaving Kaigaku out to dry. If he was going to blatantly favor one disciple, why’d he even bother with Kaigaku?

Kaigaku swore and gnashed his teeth. “KUWAJIMA!” roared Kaigaku.

“You always played favorites! Teaching the weakling another form just because he played house with you!”

Zenitsu refuted him. “You're wrong. I came up with this form myself. Gramps never neglected you, Kaigaku.” He clenched his fists and thickly admitted, “We cared about you.”

Kaigaku wouldn’t believe any of this either. Crybaby Zenitsu hadn’t mastered any form other than the first. There was no way he’d be able to create an entirely new one, much less one as impressive as this.

Kaigaku could have, however. If he hadn’t obsessed over the form that had eluded him for so long, he could’ve created a superior form that outmatched stupid Thunderclap and Flash. That stingy old fogey should’ve realized that the first form wasn’t important and picked him for the Tsuguko position.

He hated it. He hated him. He hated them all. They’d never recognized how hard he worked, how hard he trained. All those bloody hours in the training yard, worthless? Even if he had never managed that dumb form, surely his hard work and dedication meant something more than the absolute insult that was sharing a title with Zenitsu of all people. It should have meant more. He deserved better, so it was only natural for him to follow those who truly valued him. Zenitsu and Kuwajima had no right to deny him what he deserved.

As his head arced through the air, Kaigaku’s eyes connected with a familiar pair.

“It’s my first time seeing this form, but I know Zenitsu created it to fight at your side. It’s a shame you were its first victim instead.”

Two thuds occurred as Kaigaku’s head finally landed on the ground and Kuwajima descended from the nearby tree he had been perched on.


During Zenitsu’s training


It was early morning, and Jigoro was organizing his belongings. Since Zenitsu had demolished part of his house, Jigoro had packed up his most treasured possessions and taken them with him when he left to assist with training.

He had always wanted to reorganize his belongings since he’d packed in a rush, but there had never been time until now. There was a lull in training this week, so he had returned to where he roomed at HQ to tidy up and sort his belongings.

Every item laid before him was associated with precious memories. He reminisced as he arranged them. There were many fond memories, such as the ones featuring Zenitsu, but there were also items associated with bitter ones.

For example, the haori in front of him.

After Kaigaku returned from the Final Selection, Jigoro had been over the moon. He had congratulated the youth and even gifted him a blue haori patterned with triangles, a haori similar to the one he wore. It was a sign of his approval and carried blessings for luck. In hindsight, it was luck that Kaigaku sorely needed.

Jigoro sighed as he folded the haori into a small square, one that he could easily carry with him. He had been a fool. Perhaps he still was one. He should’ve known something was off based on how Kaigaku treated his master’s gift.

Kaigaku had accepted it with a smile, but he had never worn it. It had remained in his room after he departed. Jigoro had hoped that his disciple had merely forgotten to pack it as it was a new item, but now he knew.

Kaigaku likely had never cared for it. Jigoro still couldn’t comprehend why Kaigaku had subtly rejected his gift.


The present


But now Jigoro knew. It was far too late though.

The former master-student pair stared at each other. Kaigaku was too shocked to speak due to Jigoro's unexpected appearance.

Mournfully, Jigoro spoke. “I’m sorry, Kaigaku. I shouldn’t have chosen you. You were never meant to be a demon slayer. Atone for your sins in your next life and live well.”

The old man tossed something out at his former disciple.

The last thing Kaigaku saw was a very familiar haori as it fluttered down and covered everything.



It was dark, and Kaigaku was fading. He couldn’t accept it. He couldn’t just die like this. Mocked and defeated by his weakling of a junior, disowned by his former master, and covered by the very haori that he had rejected so long ago.

Kaigaku remembered the day he’d received it. He had passed the Final Selection and returned to Kuwajima’s residence to notify the old man. Instead of the Tsuguko position, he had been given a pathetic piece of fabric. After forcing a smile and accepting the mockery of a reward, he had angrily abandoned it in a place he’d never return to.

And now, the old fart was forcing it on him once more. He couldn’t even reject it this time. If he had known it was going to be the last thing he’d ever see, he would’ve incinerated it the moment he first held it. He loathed the damn thing.

He cursed the senile geezer. How dare he? He wasn’t even letting Kaigaku die in peace. He’d never given Kaigaku anything he wanted, but he’d given Zenitsu all the love and affection that coward had ever asked for.

It was unfair. Everything was unfair. He was special, and he deserved better. He was talented, but he had also worked harder than anyone. He was superior and deserved more, but Kuwajima had unfairly treated the weaker and lazier Zenitsu as Kaigaku’s equal.

Had… had Kuwajima known? Could he have predicted that one day Zenitsu would stand above him? Was that why he’d favored Zenitsu?

Either way, Kuwajima was wrong. Kaigaku should have always been chosen. He should have been the only one chosen. If he had more time… he would’ve shown them all.

If only he had more time…



Zenitsu stared blankly as the haori flattened and Kaigaku’s headless body crumbled.

He was gone. Kaigaku was dead. Zenitsu had killed him. It was over.

All the energy in his body fled, and the blonde feebly stumbled toward his Gramps. Gramps who had come out of nowhere and shut up Kaigaku with a few words and a haori. What?

Had Gramps been there the entire time? Had… had he seen and heard everything? Zenitsu wanted to know, but his vision was blurring. He was exhausted, and his body wasn’t following his commands.

He could hear his friends’ cries as he collapsed toward his Gramps who thankfully caught him.

“Gramps…” he gasped. “Sorry…the haori you gave me…”

Everything went dark as his face smushed into his Gramps’ haori.



As Jigoro lowered his unconscious child to the ground, he ruefully thought about how different the two orphans he had picked had turned out.

One ruthlessly discarded his gift. The other treasured it so much that he had instantly apologized for accidentally destroying it despite suffering from exhaustion and injuries.

Although his feelings about the outcome of the fight were complicated, Jigoro had never been prouder. Zenitsu’s creation of a seventh form displayed great mastery of Thunder Breathing despite his inability to master most of its preexisting forms.

“Well, that was a spectacular display of Thunder Breathing,” Tengen commented as he joined the slayers on the ground.

Shinobu fluttered down gracefully as well from her perch in the trees. She headed toward Zenitsu and began examining the unconscious youth.

Tanjiro, Inosuke, and Nezuko quickly approached the four. Tanjiro blurted out, “Is Zenitsu going to be okay? How long have you been here?”

Inosuke jumped in. “I didn’t feel anyone on the way here, but someone moved in the trees earlier.” He pointed at the older group. “You got here just in time, huh?”

Uzui grinned. “Yeah, we set out after you, so we arrived pretty much right when the fight started.”

The ex-Sound Hashira gave a thumbs up. “I’m glad we showed up to watch; it was a splendid fight. Quite flashy.”

Shinobu sat back from her examination of Zenitsu. She joined the conversation and said, “Zenitsu-kun fell unconscious due to his exhaustion. He’s been straining himself these past months, so he likely fainted once he saw Kuwajima-san and relaxed.”

The Insect Hashira smiled. “As for his injuries, they aren’t severe. They’re similar to the ones from his run, but they’re lighter. He won’t have to spend weeks in bed this time, most likely only a few days. In fact, he might sleep through his injuries.”

She quirked her head and added, “In a way, Zenitsu-kun’s earlier run must’ve prepared his body for this kind of strain. He paid in advance, I suppose.”

The others were relieved to hear that Zenitsu would be fine in a few days.

Uzui chuckled. “That was probably the cleanest and quickest Upper Moon fight in recent history, not that the traitor was much of an Upper Moon. Still, I can’t wait for the corps to find out.”

The former Sound Hashira smiled proudly. “He couldn’t have done it without my training.” The ex-shinobi also nodded at Kuwajima, “And yours, of course, but he defeated Upper Moon 6 in a 1v1.”

He cackled suddenly and slapped Kuwajima on the back. “You know what this means, don’t you?”

Until this moment, Kuwajima had been distracted by the death of his former disciple and Zenitsu’s physical wellbeing, but he choked up as he realized what exactly Zenitsu had achieved just now.

His precious child had slayed a member of the Twelve Kizuki all by himself.

Notes:

Zenitsu to Tengen: “Nah, I’d win.”
Questions at the end!

To clarify, Zenitsu only used the 7th form once. First section came from Zenitsu’s POV and had his thoughts, and the latter was a replay that included the perspectives of others as well.

The three of them initially didn’t notice the others arrive because they were focused on Kaigaku, a demon and obvious threat. Also, Inosuke noticed but not Tanjiro because of the wind’s direction lol.
In GS, Zenitsu has only been injured by humans (with himself as the MVP), haha. He was also the one that shredded his haori; like canon, it couldn’t withstand the 7th form’s force. Our boy did an oopsie! He trained topless, so he totally didn’t foresee this.
Tengen’s secretly a softy here. XD He’s more interested in Zenitsu in this AU because the run was impressive. Poor Shinobu came all the way for pretty much nothing, haha.
Both Jigoro and Zenitsu apologized, but note that they never said they forgave Kaigaku.
RIP Kaigaku. Given that he had a bit more motivation and time, I like to think that he strengthened the cracking effect of his canon attacks... but he never landed one because Zenitsu improved far more with his flashy new support system and drive to keep Gramps alive :P

Question(s):
Feel free to answer all, some, none, or just the one below!
Either in the comments or this anon Google Forms that doesn’t require your email (the form has some fun questions though).
Feel free to comment as usual ofc!

Not really a spoiler since it’s tagged, but what should Zenitsu’s Hashira title be?
Thunder Hashira? Rumble Hashira? Roaring Hashira?
Something different?
Thunderclap Hashira? Flash Hashira? Godspeed Hashira? Golden Hashira? Dragon Hashira? Thunder God Hashira? God Hashira LOL jk.
Give me your suggestions or pick one of the above! I’ll consider them.

Chapter 10: Zenitsu

Summary:

“I just wanted… to become a Hashira while you were alive.” – Agatsuma Zenitsu to Kuwajima Jigoro, Chapter 146.

Notes:

Sorry for the delay! I promised I’d finish this before the anime finished, and Infinity Castle releasing helped motivate me. At least it's a huge chapter compared to the rest. It's ~7k words while the others average around 2k.
Also, special character mention/cameo! Hinted at it for ages. I had to include my other fave somehow.

If you have time, check out the new survey after you finish the fic (it's also linked at the end). I also linked a Google Doc at the end with results from the Chapter 9 Survey (Feel free to take that one too before reading this chapter)! I picked his Hashira title based on the votes/comments.

Enjoy the last chapter! Thank you for all the support, everyone!
Posted 8/24/2025

(See the end of the chapter for more notes.)

Chapter Text

Contrary to Zenitsu’s expectations, he woke up feeling refreshed. When he had felt his vision failing him, he had known he was about to faint and eventually wake up in bed at Butterfly Mansion. He had thought he’d be as sore as the last time he overexerted himself, but Zenitsu only felt pure relief this time.

He had won. Kaigaku was gone, and it was over.

Gramps would live. He’d be proud.

Although Gramps had affirmed that he was proud of Zenitsu, Zenitsu hadn’t been able to believe it… until now. Zenitsu had finally done something satisfactory and worthy of being the ex-Roaring Hashira’s disciple.

A tear trickled down his cheek. He’d really done it.

Zenitsu gritted his teeth and stared at the ceiling. He wasn’t going to start sobbing because everything was finally alright. He had just proven himself worthy of being Gramps’ disciple, and he vowed that he wasn’t going to be a crybaby anymore. He took deep breaths to stabilize himself, but he still felt a bit weepy. Zenitsu reminded himself to calm down. He’d become a strong and reliable demon slayer, and he was going to show Gramps that crybaby Zenitsu was no more when he walked through the door.

Suddenly, Zenitsu realized something. The ceiling he’d been staring at was unfamiliar. This wasn’t Butterfly Mansion. The youth slowly sat up and looked around. The room was unfamiliar, but the nearby sounds weren’t. He could hear the melodious grunts from Hashira training and the hustle and bustle of HQ. He could also hear familiar footsteps approaching the room.

When Jigoro opened the door and entered the room, Zenitsu burst into tears.



It was embarrassing how Shinobu-san had seen him cry right after he’d internally vowed to no longer be a crybaby. Gramps had barely stepped in when Shinobu-san, who had been following the elderly man, began checking his condition because he’d woken up for the first time in days.

Days. At least it hadn’t been weeks like last time, Zenitsu thought. Shinobu-san had informed him that his injuries weren’t severe and that he was mainly unconscious due to exhaustion. He hadn’t been taken to Butterfly Manor since his injuries hadn’t necessitated it, and he was currently in an area HQ used for treating injuries. Before leaving, she’d smiled, patted him, and let Gramps know Zenitsu was perfectly fine now.

It was just him and Gramps in the room now.

Zenitsu didn’t know what to say. He’d just sobbed all over the old man, and his nose was still running a little. He felt like a small child even though he’d just killed Upper Moon 6. Kaigaku was gone, and some part of Zenitsu still felt a little empty.

Thankfully, Jigoro broke the awkward silence that was brewing by offering Zenitsu a plate of sliced apples.

“Eat up; you need the nutrition,” Jigoro said in that grumpy way of his.

“Ah, okay…” Zenitsu took the plate.

He crunched on a few apple slices, sneaking a few glances at his master, who had taken a seat next to Zenitsu’s bed.

All was quiet until—

“IDIOT DISCIPLE!” Jigoro smacked Zenitsu’s head with his staff.

“AHHHHH, WHAT WAS THAT FOR, GRAMPS? THAT HUUUUURT!” Zenitsu wailed, clutching his poor head. Some apple slices scattered on the bed.

“YOU LEFT WITHOUT TELLING ANYONE!” The former Roaring Hashira roared. “If you didn’t want to tell me, you could’ve told Kocho-san or sent your sparrow!”

The old man huffed. “You didn’t know how rough of a condition you would’ve been in after the fight.” Jigoro shot his idiot disciple a glare.

“It would have been pointless if you’d won but DIED because you were too foolish to leave a message before rushing to fight a strong demon! What were your friends going to do if you were severely injured? Did you think about how you would’ve worried them? Foolish child.”

Zenitsu cowered as he received an unexpected scolding. Come on, he’d just defeated Upper Moon 6! He’d come out barely scratched.

“G-Gramps, I knew I’d be fine!” He whined. Gramps looked unimpressed, but Zenitsu pushed on.

“I knew I’d win,” he said, still rubbing his head. “I was sure I’d beat Kaigaku.”

Both of them winced after hearing the former disciple’s name, but Zenitsu continued anyways. “I let Tanjiro, Inosuke, and Nezuko-chan come because they wouldn’t be in danger.”

Jigoro frowned, ready to interrupt, but Zenitsu cut him off. “I knew he would be strong, but I knew I would be stronger.”

Zenitsu remembered his conversation with Uzui during Hashira training and Rengoku facing Upper Moon 3 and spoke, “Humans are stronger than demons. He couldn’t become stronger than me in one year.”

The demon slayer looked into his master’s eyes. “He chose to lose his humanity instead of dying, but I was willing to die to save you, Gramps.” Both Thunder Breathers were starting to tear up.

Zenitsu smiled as his eyes grew moist. He shakily chuckled, “I felt like I was dying during training. There was no way Kaigaku would’ve trained as hard, especially since he’d become overconfident after becoming a demon.”

Zenitsu sighed. “Eating humans made him stronger, but he wouldn’t have changed much where it mattered. And… he would’ve still underestimated me, so his training wouldn’t have been as desperate as mine.”

“He used his Blood Demon Art with his breathing,” Zenitsu recalled. “I didn’t see him do anything but use it to enhance his forms.”

Zenitsu smirked. “He couldn’t even land a hit on me because he hadn’t managed to learn any special techniques in time.”

Jigoro raised an eyebrow. “You’re sure he didn’t have anything else?”

Zenitsu nodded. “I could hear it. The desperation in his attacks, the feeling of weakness and being unable to hit me… the panic and disbelief he felt. Kaigaku had nothing, and I had all of you training me and a new form.”

Jigoro examined his disciple. Despite the exhaustion the boy was still feeling, there was finally a sense of pride coming from his student. Zenitsu had truly grown up.

The old man grumbled. “And I almost missed seeing your new form in action, brat.”

Zenitsu perked up, recognizing this was Jigoro backing down. “But you didn’t!” He smiled cheekily.

Jigoro snorted. “No thanks to you. At least your sparrow was smart enough to let me know.”

Zenitsu’s eyes widened. “Chuntaro told you?”

Jigoro nodded and recounted what had happened. Chuntaro had noticed Zenitsu leaving with Tanjiro and Inosuke following. Inosuke wasn’t subtle. The bird had flown to Jigoro, and it hadn’t taken long for Jigoro to realize because it was the day of the fight.

After retrieving the haori, the former Hashira had quickly found Shinobu-san, who’d been treating slayers with light injuries from training, and asked her to come in case his foolish disciple needed treatment. She agreed, and they left with Uzui, who had overheard them and wanted to see a flashy fight. Jigoro left out how the former Sound Hashira had carried him with one arm as they traveled. They’d barely made it in time for the fight without Jigoro’s age and peg leg slowing them down.

The three of them had landed on the trees surrounding the clearing and immediately seen Kaigaku slashing at Zenitsu.


Moments after the fight started


Kaigaku had always been good at Thunder Breathing. Jigoro had recognized his talent and determination, but he hadn’t seen enough in the end. At least he’d see Kaigaku’s end, Jigoro mused, watching the ongoing clash below him.

The old man sighed as he stood on a tree. Below, Kaigaku was a whirling vortex of black lightning as he executed Third Form: Thunder Swarm. Zenitsu was the golden thread that weaved through the darkness, his blonde hair and yellow haori flashing through the dim light.

Jigoro would have worried had he not noticed the calmness and smoothness of Zenitsu’s evasive movements. Zenitsu, with his hand on his sword, was ready.

Shinobu gazed down at the clashing Thunder Breathers. She had noticed Zenitsu’s recent efforts and seen him grow from a loud annoyance into a slayer that no longer cowered in front of a demon as strong as Upper Moon 6. She smiled at the sight below her.

Uzui was impressed. Although he only had one eye, he was fast enough to clearly see the fight. The ex-Hashira snickered internally. The boy’s eyes weren’t even open. All their training had been worth it, and he was in for a spectacular show.

The three of them leaned forward breathlessly as a flash of light reflected off the lanterns hanging nearby.

In the dim light, Zenitsu’s golden eyes flashed as he zapped forward, but his blade shone brighter as blood was flung into the air.

Uzui chuckled, having heard what Zenitsu had whispered to the demon. Jigoro watched as his former disciple clasped a hand to his wounded neck in disbelief.

Kocho glanced at Uzui, eyes curious. The former shinobi quietly explained. “The demon called that a lucky hit even after Agatsuma called him trash and slow. The traitor said there wouldn’t be a second chance.”

Uzui’s lone eye gleamed as he smirked. “Sure, Agatsuma might need one more chance, but the demon won’t get any.”

“He’s untouchable now,” Uzui said proudly, thinking of their training sessions.

Jigoro grunted in agreement, eyes focused on seeing his pride and joy flash throughout the clearing below.

Kocho, however, smiled serenely. “I suppose I’m rather unnecessary then?” She joked before glancing down. “It looks like it’ll be over soon.”

“Indeed,” Jigoro said, as he heard his child apologize to the disciple he’d failed.

His breath was stolen as his beloved disciple performed a new Thunder Breathing form, releasing a striking golden dragon that flashed forward and across a pale throat.

Jigoro was amazed at the sight. He had never seen a breathing form as awe-inspiring as his disciple’s new form, and the emotions, not the bright flash, brought tears to his eyes. A young boy unable to perform anything but the first form had managed to somehow create his own form, one that seemingly surpassed the others. Kaigaku’s strikes had all cracked under the dragon’s force.

Jigoro watched as Zenitsu touched down, surrounded by the fluttering and falling shreds of his yellow haori. The old man jolted as his former disciple’s head roared as it arced through the air.

Kaigaku’s words stung more than any attack Jigoro had received, but Zenitsu’s voice pierced through the pain.

“We cared about you,” his disciple said. And it was true. Jigoro had always cared. He just hadn’t voiced it, assuming Kaigaku could tell from his actions and the blue haori clenched in his fist.

Their eyes met. Jigoro could see Upper Rank 6, but he couldn’t see his disciple in them. He didn’t know what those clouded eyes could see, but he knew Kaigaku’s ears were still intact. He had one last moment.

The old man left to bid his former disciple farewell, bringing the last gift he could offer.


Present


They sat in silence as Zenitsu processed his grandfather’s words. He hadn’t heard the trio during the fight due to how focused on Kaigaku’s sounds he’d been, so he’d been shocked when Jigoro suddenly appeared and threw a haori on Kaigaku.

A haori. Zenitsu startled his gramps a little as he abruptly shot up and desperately looked around.

“My haori! Where is it?”

“Zenits-” Jigoro began.

The boy gasped, cutting him off. “It—it’s gone!” He suddenly remembered how he’d apologized right before passing out. He’d shredded his haori during the fight. He’d come out intact, but his cherished yellow haori with its white triangles hadn’t.

His eyes were truly pools of water now. “Sorry, Gramps,” he blubbered. “I couldn’t protect it.”

His grandfather sighed as he wiped Zenitsu’s tears. The old man rubbed Zenitsu’s back as the boy cried.

“Zenitsu, it’s fine, so stop crying. Wipe your tears.” The old man patiently waited for his child to quiet down before reaching into his robe.

“Here,” he said. “I prepared this for you.”

Zenitsu stared. It was… his haori? A very familiar yellow and patterns he’d seen every day. He reached out and felt the fabric. It was warm and soft, and it felt like family.

Jigoro chuckled, seeing his student’s reaction. “I’m surprised your haori lasted this long. I had this one prepared long ago, and I was waiting for you to come get it.”

He rubbed his disciple’s head fondly as he continued. “There will always be more for you at home, so come back when you need another.”

Zenitsu’s tears started up again because he’d understood what Jigoro had said. He’d cherished the last haori because it was a gift from Gramps and because it was a sign that he belonged and was cared for, but now Gramps had offered him even more.

They’d been family for a long time, but Gramps had just directly offered him a home. A home that he could go back to forever.

He clutched the haori tightly as happy tears rolled down. “Don’t get it wet, boy,” Jigoro grumbled. “Just because you can always get more doesn’t mean you shouldn’t take care of it.”

Zenitsu ignored those words (he’d follow them later) as he crushed the haori and his grandfather against his chest in the biggest hug he could give.



Zenitsu was wearing his new haori over the pajamas he’d been wearing. He’d put it on and promised himself that this one would survive. He’d even thought about sneakily getting a replacement from Gramps while keeping this one as a memento.

Gramps had chuckled, seeing him sparkle as he donned the haori. Zenitsu was over the moon. He’d won the fight, reclaimed his master’s honor, used his flashy new form, and received a haori, home, and hug from Gramps, who was definitely proud of him. Zenitsu couldn’t be happier, and he knew his Gramps was happy too.

The door slammed open, and Zenitsu choked as a pig-headed varmint smashed into him.

“MONITSU!” “ZENITSU!” His friends cried as they piled into the room. At least Nezuko-chan was quiet. She was the best.

“You’re awake!” Tanjiro said, wrestling Inosuke off Zenitsu. Bless him. Screw Inosuke.

“INOSUKE!” Zenitsu shouted. “What was that for?”

“A fight! I challenged you ages ago! You’re done with the demon, so it’s my turn now!” Inosuke announced, bouncing excitedly with his swords already out. He was pleased that Zemitsu had grown strong. He would be fun to fight. Inosuke had seen the golden dragon and decided it was an opponent worthy of the King of the Mountain.

“NOT NOW!”

“NOW!”

Jigoro watched as Zenitsu squabbled with his friends. Poor Kamado-kun. His friends were a handful. And loud.

Thankfully, the boy had it under control with a brutal headbutt to Inosuke’s head. The old man idly wondered if the boar mask provided any defense.

Tanjiro brightly continued congratulating Zenitsu and gushing over the fight and Zenitsu’s new form while Inosuke rolled on the floor in pain. Zenitsu was blushing, Jigoro noted. At least he didn’t seem like he was going to cry again.

The door slammed open once again. “Boys!” Aoi scolded. “Didn’t you say you were going to get the sleepyhead? It’s almost time!”

Although he had no idea what was going on, Zenitsu joined Tanjiro and Inosuke in instinctively cowering from Aoi’s wrath.

“Sorry, Aoi-san! We’ll get them there right away.” Tanjiro recovered and smiled at the girl.

“Yeah, I’ll take Zanitsu!” Inosuke popped up and grabbed the protesting blonde. He charged out of the room with his captive thrown over his shoulder.

Aoi blinked. “Does… he know where to go?”

Tanjiro shrugged. Aoi sighed, deflating. “I’ll take them to the meeting.” She bowed toward Jigoro and left. The two left in the room could hear her running and shouting in an attempt to catch up with a long-gone charging boar. They pitied her, but they pitied Inosuke more. She was going to be pissed.

Tanjiro turned to Zenitsu’s master. “There’s a Hashira meeting in a few minutes, Kuwajima-san. We were supposed to fetch you and Zenitsu, but we got a little distracted.” He smiled sheepishly.

Jigoro nodded and stood up. “Let’s go,” he said gruffly. “I’m looking forward to the meeting.”



Zenitsu wanted to puke. It would serve Inosuke right to get puked on, he thought darkly. The idiot deserved it.

At least an angel had rescued him from the monster giving him the shakiest ride of his life. Aoi had terrorized Inosuke before leading them to the right room. Thankfully, he’d been allowed to walk this time.

Zenitsu still felt like puking. Why were all the Hashira here? Why were they all looking at him, some guy in his haori and pajamas? Even some retired Hashira were there. Ugh, Uzui looked so smug. The bastard definitely knew what was happening.

Man, he was in pajamas in front of all the Hashira and what appeared to be the boss’ wife. She was beautifully elegant, and he was in pajamas. His eyes were probably also red from crying, and he didn’t even know the state of his hair after Inosuke’s chaotic carry. At least his haori looked good. He smoothed it and felt comforted by the familiar sensation.

Tanjiro and Gramps soon entered, and Zenitsu glared at his friend. He’d known a meeting was coming, and he didn’t warn Zenitsu. Look at him being all put-together while Zenitsu was in his pajamas in front of the corps’ higher-ups.

His head whipped around as Ubuyashiki-sama spoke. “Now that everyone has arrived, the meeting will begin.”

“This meeting has been called to discuss the matter of former Hashira Kuwajima’s defected disciple, Kaigaku. We received notice of his betrayal about a year ago but allowed Kuwajima-san to remain and train the corps during Hashira training.”

She glanced at Zenitsu, who suppressed an eep. “The corps allowed this because his other disciple, Agatsuma Zenitsu, swore to reclaim his master’s honor through defeating Kaigaku in a year’s time.”

Zenitsu could feel the room’s eyes on him and shivered. This was scary. Perhaps Ubuyashiki-sama could sense his discomfort because she smiled gently at him. “We have been notified of the victory, but the corps would like a detailed report about the duel and its outcome from the people directly involved. Agatsuma-san, please speak.”

Zenitsu froze. A report. He was to report his fight with Kaigaku. He opened his mouth. Closed it. Everyone was waiting. Tanjiro looked as if he wanted to help, but he stayed silent since it had been Zenitsu who had been directly addressed.

Tengen groaned internally. This was going nowhere, he thought. Agatsuma had frozen, and it didn’t seem like he’d thaw anytime soon. Ubuyashiki-sama looked concerned, but she wasn’t pushing since she knew she’d probably terrify the blonde more. He knew Jigoro-san was also worried but unable to speak since this was technically his trial. Surprisingly, the boar-headed brat was staying silent, but that was probably due to him still recovering from whatever the Butterfly Girl had just done to him.

Tengen knew it was up to him then. It was improper to interrupt, but he figured someone had to do it before Agatsuma passed out or Sanemi exploded. He sighed. “This is so unflashy,” he spoke, breaking the awkward silence. “Agatsuma,” he called. “Where’d all your flashiness go? You were flamboyant enough during the fight.” He gave the blonde a condescending look.

As Tengen had predicted, the boy bristled, thawing instantly due to his rage. “Oi—”

Jigoro coughed. The young slayer paused and seemingly remembered where he was. “Oh.”

Zenitsu blushed. Ubuyashiki-sama smiled at him. “Please continue, Agatsuma-san. We would like to learn more about the fight.”

Zenitsu nodded rapidly, still red. “Y-yes! On the day of the fight, I left early, and Tanjiro and Inosuke followed me with Nezuko-chan in her box. We arrived around dusk. The sun hadn’t set yet, so we checked the area for demons and hung lanterns around a clearing.”

Zenitsu paused. “I don’t know how long we waited, but it felt like it got dark quickly. I heard his sound, and he entered the clearing.”

Ubuyashiki-sama looked curious. “Could you clarify what you heard? His sound?”

Zenitsu flushed. “I have good hearing. Uh, a bit like Uzui-san, so I heard the sound of a demon and his footsteps.”

Some of the Hashira looked curious but stayed silent to respect Ubuyashiki-sama and the formality of the meeting. Tengen just looked smug from Zenitsu being forced to refer to him respectfully. Ubuyashiki-sama nodded and gestured for him to continue his story.

Zenitsu took a couple seconds to remember where he was at before continuing. “He still looked somewhat like a human, but he had markings on his face, and his eyes were brighter.”

“His eyes said Upper Rank Six.” Zenitsu jolted as the room erupted.

Apparently, not all the Hashira had heard the others’ accounts of the fight. Some of them looked visibly shocked, and Zenitsu winced at the noise level.

He wasn’t the only one annoyed by the uproar though. “SHUT UP!” Tengen roared above the rest. “LET HIM CONTINUE!” He huffed as everyone quieted down. “It only gets flashier from here,” he grumbled.

Ubuyashiki-sama smiled and thanked Uzui for keeping the meeting on track. Everyone’s attention returned to Zenitsu, although some looked as if they wanted to assault him with questions.

Sensing some of the Hashira’s disbelief, Zenitsu repeated himself. “Kaigaku was the new Upper Moon 6. The first thing he did was mock me, so I told him he was wrong.”

Inosuke, uncaring of propriety and finally recovered from Aoi, interrupted. “Now that you’re a demon, you have no right to call me weak,” he said, making a weird face (was that supposed to be him?) and quoting his words.

Loud applause came from the corner where the retired Flame Hashira knelt. The other retired Hashira next to him shushed him.

Zenitsu shot Inosuke a dirty look for the terrible imitation but continued without commenting. “He asked if I’d learned any new Thunder Breathing forms, so I countered by asking if he’d learned the first yet.” Someone chuckled.

Zenitsu fidgeted. “I’ve never been able to use the second through sixth forms of Thunder Breathing,” he admitted.

Shinazugawa finally couldn’t hold back his disbelief. “And you’re saying you beat Upper Moon 6 with only the first form?”

“No! Besides,” Zenitsu added, “Kaigaku never managed to learn the first form. He only knew the second through sixth.”

“And,” Zenitsu smirked. “I never said I only used the first form.”

Before any more interruptions could occur, he continued. “I then called him the weakest Upper Moon. I heard his anger, and he said he was the seventh-strongest demon and that I’d be dying that night.”

Zenitsu clenched his fists. “I asked him why he betrayed the corps.”

The slayer glanced at the former Roaring Hashira. “He said he didn’t care about us and insulted my master. I called him a scumbag and told him he was the one who should die. We… exchanged insults for a bit until he got angry enough to attack.”

The listeners grew excited, sensing the action was about to start. Zenitsu didn’t notice, but Uzui’s single eye sparkled in excitement.

“He said he was special and called me nothing compared to him. He used the fourth form of Thunder Breathing at us, and we all dodged. The others backed off, and I continued dodging his attacks.”

Zenitsu paused, trying to remember more. “I was focusing on dodging and figuring out how much he improved.”

Uzui smugly added, “And your eyes were closed.”

There were some murmurs in the room. Zenitsu flushed. “I was trying to focus on listening to him!”

“And what did you hear?” Ubuyashiki-sama asked.

“He was angry,” Zenitsu said. “Really angry. What I said must’ve really gotten to him.”

“He… didn’t really feel different. It sounded like he didn’t change much,” Zenitsu admitted. “His Blood Demon Art enhanced his Thunder Breathing, but it still sounded like Kaigaku, and he only used Thunder Breathing forms.”

Zenitsu took a deep breath. “He hadn’t changed enough, so I knew I’d win. I could hear his intent, where he’d strike, and how the blows would land.”

“I’ve been training my speed, so I dodged every blow.” Zenitsu smiled. “He was surprised and grew afraid. His attacks weren’t landing even though their range increased because of his Blood Demon Art.”

Zenitsu frowned, focusing. “I heard a strong flash of fear before he grew confident again. He called me a coward for only dodging, so I used his distraction and used the first form.”

“I nicked his neck,” Zenitsu recounted. “It was shallow, and he recovered.”

Zenitsu rolled his eyes. “He called it a lucky hit.” Someone in the room scoffed.

“He used more forms; the second, third, and fifth, I think. I dodged them again and waited for an opening.”

Zenitsu took a deep breath. “And then I used the seventh form.”

Ubuyashiki-sama looked surprised. “I thought there were only six forms of Thunder Breathing?”

Zenitsu glanced at Gramps and noted the proud look on his master’s face. He sat up straighter. “I created a new form, Flaming Thunder God.” Zenitsu flushed and wondered if the name was too much.

Tengen crowed, “And it was one of the flashiest things I’ve ever seen!” Some of the Hashira were surprised at Tengen’s sudden exclamation. Tengen had high standards for flashiness; most knew.

Inosuke chimed in. “It was a dragon! A yellow dragon made of lightning!” His hands blurred as he mimicked the dragon.

Zenitsu scowled at the interruptions, although he was secretly pleased. “I dashed forward in a low stance and slashed up at his neck.”

Zenitsu grew somber as he remembered Kaigaku’s death. “His head flew off. Before he died, he… he blamed Gramps and thought that Gramps had taught me a form he kept secret from Kaigaku, so I told him I had created the form.”

“I didn’t know Gramps, Uzui-san, and Shinobu-san were there, but that was when I saw Gramps appear. I wasn’t injured, but I was out of it after the fight, so I don’t really remember what they said to each other. I saw Gramps cover Kaigaku with a haori, and his body disappeared. I passed out soon after,” Zenitsu admitted.

Everyone looked toward Kuwajima for clarification. The old man drew himself up and recounted his last words to his former disciple.

Shinobu’s bright voice dispersed the room’s growing somberness. “And then, I checked Zenitsu-kun for injuries. I was present because Kuwajima-san had asked me to come in case Zenitsu-kun needed medical attention after the fight. We set out shortly after them,” she explained.

Tengen added, “And I came for a flashy fight!” but everyone ignored him, causing him to pout.

Shinobu continued, “Zenitsu-kun was uninjured, having dodged every blow.”

Ubuyashiki-sama nodded at Zenitsu. “That was quite impressive, Agatsuma-san.”

“Thank you,” a flustered Zenitsu responded. Praise from a gorgeous lady! Hell yeah!

“Yes, very impressive.” Shinobu acknowledged, causing Zenitsu to preen even more. “He had fainted from exhaustion, so we took him back to headquarters to rest. He indeed required no major treatment and woke up a few hours ago.”

Ubuyashiki-sama smiled. “Excellent report. Thank you for the information, Agatsuma-san, Kuwajima-san, Kocho-san.”

She calmly gazed at everyone in the room, and they leaned forward in anticipation. Something momentous was coming.

“This generation, the corps made several major breakthroughs, such as the defeat of several Upper Moons.” She nodded toward those who had defeated the demons.

“But,” she paused. “This was the first time an Upper Moon has been slain singlehandedly by a non-Hashira member of the corps. At least in recent years.”

Someone gasped, realizing, and she smiled. “I acknowledge that the demon was only recently promoted, but this remains a great victory, and we must treat it as such.”

Zenitsu fidgeted, not knowing where this was going. Everyone’s eyes were piercing him, more so than before. He knew he’d reclaimed his master’s honor and defeated a strong demon, but the way they were reacting… Why did it feel like he was about to be punished? At least Ubuyashiki-sama was clearly pleased.

Zenitsu subtly looked at Gramps. He looked… like he was about to cry? That only worried Zenitsu more, and he prayed for Ubuyashiki-sama to put him out of his misery.

“Agatsuma Zenitsu,” she announced. “Has defeated Upper Moon 6, a traitor to the Demon Slayer Corps, and reclaimed his cultivator’s honor through single combat, as confirmed by Kocho Shinobu, the Insect Hashira, Uzui Tengen, the former Sound Hashira, Kuwajima Jigoro, the former Roaring Hashira, and other members of the corps.”

“From this moment onwards, Agatsuma Zenitsu shall be known as the Thunder Hashira.”

It was as if lightning had struck him again. Zenitsu couldn’t hear beyond the roaring in his ears.

He only jolted out of his shock when he was roughly tackled by his two friends. “...may his victories illuminate the corps’ path forward,” he vaguely heard Ubuyashiki-sama say. There was something squashed under him, a new uniform with different buttons?

“HUH?” He very intelligently said, as he laid under Tanjiro and Inosuke. Nezuko-chan patted his head.

Tanjiro had started shaking him, and his poor head rattled back and forth as he stayed limp due to shock. At least Inosuke wasn’t attacking him anymore… It looked as if he was doing some primitive victory dance around him and Tanjiro. The Hashira in the room were celebrating, although some still looked as shocked as Zenitsu felt. Kanroji had clung to a stunned Iguro and was shaking him like Tanjiro was shaking Zenitsu. Himejima was sobbing loudly while Muichiro smiled at Zenitsu and patted the Stone Hashira’s back. Shinobu-san was also smiling at Zenitsu, and it would have been enough for him to normally blush, but he was distracted at the moment. The Water Hashira’s stillness looked out of place next to the enthusiastically celebrating retirees next to him. They were really loud. Shinazugawa… he looked angry and like he wanted to protest, but he also sounded complicated. He was… happy? Zenitsu couldn’t tell through all the noise.

Zenitsu suddenly felt warm. Tanjiro had handed him over (like an infant! Rude.) to Gramps, who was… crying. Gramps was crying. Holy cow.

“Zenitsu, you are my pride and joy. I knew you could do it,” Gramps whispered as he embraced his successor.

Zenitsu was once again crying for the nth time that day. He didn’t really understand what was going on, but he knew he was happy.

He hadn’t failed Gramps, and Gramps was still here.



The rest of the day was a blur for Zenitsu. The meeting had ended, and he’d nodded through various congratulations from the Hashira, but he didn’t remember much besides how weird some of them had been. He did remember clutching his Gramps’ hand throughout, and that would’ve embarrassed him if he wasn’t so happy Gramps was still by his side.

After the retired Flame Hashira had started the Hashira encounters by loudly congratulating him, Shinazugawa had suddenly been in his face. Zenitsu had flinched back. “Nice job. Don’t let this get to your head though,” the man snarled before stomping off. He still sounded weirdly happy, so Zenitsu shook off his terror.

Obanai had accosted him next. “Ubuyashiki-sama asked me to inform you that your pay was increased, but you won’t be receiving the increase until the damages have been paid off.” What? What damages? Zenitsu’s confusion was only increasing.

“You did great, Zenitsu-kun!” Kanroji smiled, blessing his eyes, as she followed Obanai.

Tomioka had nodded and muttered, “Congratulations,” before drifting off.

Muichiro hadn’t said much to him because he was still accompanying a still-sobbing Himejima, who had kindly congratulated him and wished him well through his tears, but Zenitsu had heard the Mist Hashira’s approval. Genya had shown up to congratulate Zenitsu too. He’d slapped Zenitsu on the back in congratulations as the three left.

Shinobu-san had checked in to see if Zenitsu was still feeling well, considering he’d been unconscious for a few days. She also left after congratulating him, and Zenitsu was in awe because he had received a real smile from her.

He was still in a daze, but he felt content knowing Gramps was going to be proud of him forever. Take that, Kaigaku. He’d won in the end and proved that Gramps was right to take him in.

Gramps was still next to him… in this unfamiliar bustling room. What? Where was he? What was going on?

It was a large room, and he’d never been here before. How many hours had passed? It was dark, but the room was lit by multiple multicolored lanterns. There were decorations, and as he listened, cheerful chatter was abundant alongside pleasant music.

It reminded Zenitsu of a festival. An indoor festival? Wait, that was a-

“Zenitsu!” Tanjiro exclaimed, popping up next to him. “Isn’t it a lovely party? What do you want to do?”

“Food!” Inosuke didn’t wait for Zenitsu’s response, abandoning them for tables across the room that were stacked high with food.

“What?” Zenitsu shouted, trying to make himself heard through the noise.

“WHAT DO YOU WANT TO DO?”

“I HEARD YOU THE FIRST TIME, TANJIRO!” He yelled back. “What’s going on?”

Jigoro chuckled. Tanjiro beamed at Zenitsu. “You didn’t hear?” He teased the blonde. Zenitsu shot him a grumpy look, and his friend laughed.

“We’re celebrating your promotion! While you were sleeping, HQ was planning a party. It’s good for morale,” he added.

“And you deserve it, Zenitsu! Let’s celebrate; what do you wanna do?” He peered across the room. “Should we check on Inosuke?”

Zenitsu figured that Inosuke’s table manners were horrifying enough on a normal day, and he didn’t want to see what the boy would be like during a party when everyone was celebrating wildly.

Tanjiro read the disgust on his face well enough and chuckled. “I’ll leave you with Kuwajima-san then. I should probably go check on Inosuke,” he said, ever the big brother. Nezuko-chan followed her brother toward the chaos. “Be back soon,” he called. “Enjoy yourself, Zenitsu!”

Zenitsu gulped as the people around him suddenly turned to him, having heard his name. He was instantly swarmed, and he would’ve been alarmed about losing Gramps’ hand had he not seen the old man deftly escaping the mob and heading toward Urokodaki-san near the wall.

There were so many people! How many slayers were present at this party? There were kakushi too. It didn’t help that it felt like a third of the partygoers were currently mobbing Zenitsu as they congratulated him.

“Congratulations!” “Hashira-sama!” “Wow, you killed an Upper Moon!” “Flaming Thunder God!” “You really showed that traitor!” “Thunder Hashira!” “Agatsuma!” Various voices cheered and shouted.

One voice stood out to him because the words were so confusing. “You’re as cool as I thought you’d be! As expected of the slayer who destroyed Market Day by slaying a demon in broad daylight!” The swarthy slayer cackled, and Zenitsu wondered if the guy was already drunk. He couldn’t check as he was suddenly lifted by the crowd.

It was nice when he noticed women cheering for him, but Zenitsu felt like a doll as he was carried by the crowd and even tossed in the air a couple times. He could see Tanjiro, the bastard, laughing and cheering as Inosuke danced on the table next to him.

How was he going to escape? He’d already been shaken enough today. What if they dropped him? He wasn’t sure his head could take another hit either. He’d just woken up today, dammit. Huh, at least he wasn’t in his pajamas anymore. He was wearing his haori and new uniform. It was disturbing to think about who had changed him.

He was shaken out of his thoughts by an unexpected savior swooping in and abducting him.

“Saving the best ones for last, Agatsuma?” Uzui Tengen boomed, scattering the crowd with his flamboyant personality and intimidating size. Zenitsu begrudgingly thanked the former Hashira. Internally, of course.

“What?”

“You haven’t greeted the god of flashiness and festivals yet!” He posed, somehow still balancing the sake he was holding.

“Why would I do that?”

Tengen grinned. “My training paid off, didn’t it? You won in the most spectacular manner!”

The man chuckled. “I almost couldn’t believe my eye! You’ve come a long way since your time as a courtesan!”

Zenitsu groaned at the reminder. “Shut up.”

He was ignored by the flamboyant man. “You haven’t come to pay your respects to the one who helped you train your dodging. How ungrateful.” Tengen raised a white eyebrow smugly.

The young slayer made a disgusted face. Ignoring how he’d been physically unable to because of the mob, he responded, “Ew, no. You’ve been next to him all night. How can you stand it when he eats like that?” Zenitsu had been tempted to escape to the empty area surrounding the two former Hashira, but he decided to spare his ears.

Uzui shrugged. “I scolded him the first few times. He tried being quieter when eating around me, but I used earplugs for a while until he adapted. You also get used to it eventually.”

The man drank his sake. “He toned it down because of my hearing. He’ll probably do the same for you once he gets used to your hearing being like mine. Besides, it’s kinda endearing once you get used to it! The small ‘umai’ are cuter than the ones making your ears bleed.” He grinned.

Zenitsu was unimpressed but still grunted, “Maybe I’ll see him when he’s done eating.”

“That’ll take some time, even if he did recently recover. It’s been a while since he’s had sweet potatoes.” Uzui changed the subject.

“Anyways, you might be the weakest Hashira ever, but you deserve the title, Agatsuma. You worked for it, and you earned it. Congrats!”

Zenitsu gaped. Wow, Uzui must have been drunker than he thought. “Thanks, I guess.” He added, “For everything.”

Uzui just laughed and slapped him hard enough on the back to knock him over. “Show me your flashy form again later,” the former Sound Hashira said as he left Zenitsu lying on the floor.

Thankfully, Tanjiro rescued him from the floor before a mob could reform around him. “Zenitsu! I got your favorites for you!” His friend handed him a plate and a drink, which Zenitsu accepted gratefully.

“Thanks, Tanjiro.”

Tanjiro beamed. “Are you enjoying yourself? It looked like you had a nice conversation with Uzui-san!”

Zenitsu grunted as he ate his food. “It also looks like you had a fun time with Inosuke,” he retorted.

Tanjiro laughed. “Maybe I should’ve asked Uzui-san for help with getting him off the table. He instantly floored you.”

Inosuke, having sensed he was being discussed, appeared next to them with Nezuko in tow. Naturally, Zenitsu gave his complete attention to lovely Nezuko-chan and fluttered around her. Also naturally, Inosuke kept being Inosuke even at a party at HQ.

“Zeniitsu! You’re strong now! Fight me,” he shouted, shoving his way in between Zenitsu and his goddess. Zenitsu was pissed off at the interruption, but he was also surprised that that was the closest Inosuke had ever gotten to his name.

“I’ll win and become a Hashira too!”

“Inosuke, that’s not how it works,” Tanjiro butted in gently.

“Who cares, Manjiri. Let’s fight!”

“No,” barked Zenitsu. “I’m not fighting you, especially not at a party!” He was aware of the many eyes interested in their loud conversation. This was embarrassing.

Luckily, Tanjiro intervened. He must’ve known Zenitsu was having an overwhelming day. “Inosuke, you can spar with Zenitsu later. He’s tired today.”

The sunny boy optimistically announced, “We’ll become as strong as Hashira after just a little more training! We’ll catch up soon, Inosuke. Don’t worry about it.”

“Hah? I’m not worried!” Inosuke protested.

“Great! Then you won’t mind waiting until tomorrow,” Tanjiro said.

“Tomorrow?” Zenitsu groaned after Inosuke agreed and left for more food.

“Maybe he’ll forget about it after the party?” Tanjiro sheepishly offered.

“Yeah, right.” Zenitsu deadpanned. Tanjiro laughed.

“Sorry, sorry.” He smiled at his friend. “Zenitsu, Inosuke isn’t the only one who wants to challenge you. I’d like to spar when you have time too!”

“Eh, you too, Tanjiro?” Zenitsu screeched. “Inosuke’s already gonna beat me up!”

Tanjiro gave Zenitsu a small shove. “Don’t worry, I won’t pick the same day as Inosuke. I’ll be patient.”

Zenitsu sighed and gave up. His friends were stubborn. “Fine. Don’t go too hard on me though.”

Tanjiro opened his eyes wide in a pitiful way. “But, Zenitsu!” He gasped dramatically. “You’re so strong! A Hashira now!” They both cracked up at how silly Tanjiro sounded.

“Seems like you’re enjoying the party,” someone fondly said.

The two recovered and turned to see Jigoro. “Kuwajima-san!” Tanjiro greeted the old man. “I saw you speaking with my sensei earlier. Do you know where he is? I should go see him.”

Jigoro pointed out where the other cultivator had been earlier, and Tanjiro cheerily left the Thunder Breathers.

“Zenitsu,” Jigoro said, turning toward the youth.

“Gramps,” Zenitsu smiled, pleased to see him again.

The old man harrumphed. “It’s too loud in here for an old man like me. Take me outside,” he demanded.

It took a while, but Zenitsu managed to lead his grandfather outside. It was a beautiful night, and the stars glittered in the sky next to the round moon. It didn’t sound very peaceful though, since the party’s noise was audible even as they reached a bench overlooking a garden.

“Finally, some peace,” commented the elderly man.

“Mm,” Zenitsu agreed. “It hurt my ears until I got used to it. They were really excited,” he shivered, remembering how everyone had swarmed him.

Jigoro barked out a short laugh. “I’ve never seen anyone fly so high,” he said.

“Gramps!” Zenitsu whined. “It was scary! What if they dropped me!”

“No disciple of mine would die from being dropped by his comrades!” Both of them went silent as they remembered another disciple who died.

Jigoro turned to face his only student. “I’m sorry, Zenitsu.” He bowed his head toward Zenitsu. Astonished, Zenitsu grabbed his cultivator’s shoulders.

“Gramps…” he said, hesitantly.

“I made mistakes with Kaigaku,” the old man admitted. “And you suffered for it.”

“Still,” the old man said, gazing directly at Zenitsu. “Thank you. Thank you for being my student. I will always be proud of you.”

It took a while, but this time, Zenitsu’s eyes remained unwavering and clear as he faced his master. “I… really wanted you to see me becoming a Hashira.”

The boy looked up at the moon. “It doesn’t feel quite real yet, but… I’m glad you’re still here, Gramps. Thank you for choosing me.”

He gripped Jigoro’s shoulder tightly. “I fulfilled my promise to you. A year ago, you promised me that you wouldn’t die for honor if I succeeded.”

“You…” Zenitsu swallowed. “You can’t die now that I’ve become a Hashira either, Gramps.”

Jigoro examined the child he’d raised. He’d grown so much, Jigoro thought wistfully. So young, yet already a Hashira. “Wasn’t thinking of it,” he responded gruffly.

He gently rapped his idiot disciple on the head. “It’s not over yet, boy! What kind of Thunder Hashira only knows two forms of Thunder Breathing!”

Zenitsu flushed. “That said,” Jigoro added more softly, “the seventh form is amazing, Zenitsu. I’ll remember that moment forever.”

He chuckled. “Even if you never learn the other forms, you’ll be remembered for creating a new form. Not every Hashira does that.”

“You may not have mastered Thunder Breathing completely, but you’re the Thunder Hashira now,” Jigoro beamed.

“Go out and show the world who you are, Zenitsu. You’ve already made me proud, and I need to show those old coots how impressive my only disciple is. Hashira already!” He guffawed. “Not too shabby, eh?”

Zenitsu nudged his Gramps. “Fine, but I’m going to visit you often. You better have enough haori for me.”

“Of course.” The two shared bright smiles. “Don’t forget to write too, Thunder Hashira.”

...

“YOU NEVER RESPONDED TO MY LETTER, BRAT!” The former Roaring Hashira could be heard roaring at his grandson, the newly ascended Thunder Hashira, for kilometers.

Notes:

I’ve read at least 10k+ fanfics and posted 3 (the other 2 are Genshin oneshots), but this is the first one I’m truly proud of. Though, I’ve recently started writing a JJK Choso time travel fic… idk if I’ll ever post it though. (EDIT: I do have an idea for a sequel, but I doubt I'd write/post/finish it anytime soon. See the Gdoc linked below for a summary if you want.)

Thank you for supporting this fic! It really means a lot to me; I’ve never had so much engagement before. I appreciate every single one of you who gave kudos, commented, subscribed, or bookmarked! Shout-out to those who commented multiple times. Also, I’d like to thank Zenitsu for being so relatable that he wrote himself. I really needed the push.

>>>Check out this survey about the fic! I’d like to learn more about your experience with the fic, and I appreciate constructive criticism (feel free to comment it too). The fic is anonymous (no emails required) and every question is optional, meaning it could take you as short as 1 minute (or longer if you feel up for sharing). I'll keep it permanently open!
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>>>Also, here’s a Google Doc with more of my thoughts (this author’s note would be even longer otherwise), Chapter 9’s survey results, and short outlines of other fics in this AU. I also have some (mainly Gen Zenitsu) DS/KNY fanfic recs listed there.
If you want to create something inspired by the fic or translate the fic, please let me know in the comments!

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Thanks for everything! Stay awesome, everyone.

Notes:

I hope you liked it! This is my first multi-chapter fic, and it's for a series I haven't really watched and read! Years ago, I read a little bit of the manga, but I think I stopped around Tanjiro's training with Urokodaki. Got a little bored, haha. Never even met canon Zenitsu outside of YT clips. I probably would've stuck around if he had shown up earlier. Heck, if Rengoku showed up, you betcha I would've fallen to my knees in a Walmart.

I'm new to writing fanfics, so I'd appreciate constructive criticism! Please be gentle? XD Also, let me know if I'm using names/honorifics wrong. I haven't read much of the source material, so I don't really know what people call each other. I'm doing my best!

Also, please don't feed my work to AI! Thank you.

Feel free to comment, ask questions, and chat! Also, if you want to translate this or create something inspired by this, we can chat in the comments.

(Skip this if you already read the above author's note! Thank you for reading them!)
Check out this anonymous survey about the fic!
Also, here’s a Google Doc with fic-related content (more of my thoughts, fun facts, outlines of potential fics, etc.)

Thank you for reading! Have an awesome day.