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2025-05-25
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1/1
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Precious Oaths

Summary:

In an alternate universe, the boys of BTB are struggling to defeat a dungeon, and when Kaelix suddenly loses consciousness from a lack of mana, the others have to figure out if they'll make it out alive.

Notes:

This is my first Nijisanji fic, and what better way to pop into this fandom than by making a BTB AU? This was inspired by this tweet https://x.com/ver_crepuscule/status/1925767004469743748

So, thank you to Vemy for giving me brainrot!

Work Text:

The world around Kaelix seemed to be spinning as he tried to focus his attention on his teammates before him. He felt his mana depleting quickly, but the monster in front of them was still holding strong against his members, they were all nursing various wounds that were only looking worse by the minute. Zeal’s left arm swung helplessly by his side, blood dripping from his fingertips as he turned around his battle axe, trying to keep his balance as he spun. Freo was trying to gauge the distance between him and the monster, but the limp he had made it harder for him to move in a way that distracted the beast. Seible’s whip was cracking wildly as he tried to keep the monster a reasonable distance away from his injured teammates, the back of his head oozing red as he swayed. Kaelix tried to step forward to warn the others, but he felt his vision darkened, and before he knew it, everything disappeared.

THUMP

The other members whipped around, hearing the thud against the ground, and were shocked to see Kaelix, his body full of wounds, lying lifelessly on the ground.

“GRAB HIM, WE’RE RETREATING.” Freo’s voice was dripping in panic as he threw one last dagger at the monster and turned to run.

Zeal and Seible couldn’t disagree as they were too injured to protect Kaelix and defeat the monster. Zeal grabbed the mage from the ground, not caring for his left arm, he was too caught up in the adrenaline to feel the pain. Seible was helping Freo run as he was sporting a broken leg.

“AUGHH!” Zeal’s voice rang out amongst the chaos as he felt a pain like electricity run down his back.

“Zeal, what’s wrong?!” Seible’s voice called out to the taller one as he tried to look back.

When Seible was finally able to look, he saw Zeal still running, but his grip on Kaelix had weakened considerably, and the grimace on his face worsened. There was no apparent wound on the front of him, but Seible could tell Zeal was struggling. He grabbed something from his bag and let out a shout,

“DUCK!” Before Zeal had time to register what was being said, he instinctively dropped his head with enough time to hear the explosion behind him.

The monster growled at them but didn’t pursue further, the explosion cutting off the only entrance. Freo sighed in relief as they managed to exit the dungeon; not knowing how the others were, he whipped his head around. They had all made it out alive, but their wounds were becoming worse by the minute. Zeal dropped to the ground, tightening his hold around Kaelix as he looked up at the others in a panic, the wounds he received now irrelevant.

“He’s–please…I can’t–I don’t know if he’s breathing…” His voice was hoarse from screaming, but now even more so as he sobbed.

Freo looked at Seible, “Teleport us back to town quickly.” His voice trembled, but he tried to steady it as he commanded the brunette.

Without a second thought, Seible grabbed Freo and Zeal’s hands and began to chant a spell, and soon they disappeared.

- - - - -

When they teleported into town, they were thrown into the middle of the plaza, Seible unable to control where exactly they landed. Townspeople gasped and whispered as the adventurers' guild was quickly called to help them. They were all swiftly escorted to the medical center in the town and treated for their wounds, Seible and Freo having the lesser injuries of the four. When they were done getting patched up, they both went to check up on the other two. Zeal had refused to leave Kaelix’s side, even refusing treatment until he knew that Kaelix was stable. He quietly sat in the corner of the room, looking at the doctors as they rushed in and out and hooked Kaelix up to various mana infusion machines while also treating his wounds. Seible and Freo both moved over to where Zeal sat,

“You have to get treated, too, Zeal,” Seible stated matter-of-factly.

“Not until Kaelix is okay. I don’t want them wasting resources on me.” Zeal’s breathing was uneven as he struggled to speak.

Freo sighed and slapped Zeal on the back, which caused him to tense up in pain and double over in the chair. Freo grabbed a dagger from his bag and gently tore Zeal’s shirt. What he saw made him almost gag. Zeal’s back was covered in blood as a large gash from his upper right shoulder down to the left side of his waist adorned it. The scream they had heard earlier was Zeal getting whipped by the monster, and it took out most of his back. Now that the wound was finally getting air, the raven-haired man felt the pain. He gasped for breath as he hugged himself, trying to get more air but failing. Freo’s eyes widened in shock. Zeal wasn’t one to show pain, but seeing him doubled over as he choked back sobs was enough to make Freo gasp. Seible moved quickly as he grabbed one of the doctors,

“I need you to get another set of doctors here and treat my friend. NOW!” The anger in his voice was enough to send the doctor into a frenzy.

Zeal was quickly escorted into another area by several doctors, but as he was being escorted away.

“Please save Kaelix. Even if I don’t make it.” He was whisked away.

- - - - -

Kaelix opened his eyes and let out a small groan, sunlight peeking through the window. Before he could fully acclimate to his surroundings, he was engulfed in a hug. The scent was familiar, petrichor, but with a hint of alcohol. Kaelix instinctively hugged back,

“Zeal…”

The older man let go of the hug, and Kaelix saw his face. Anger, relief, worry, gratitude, and anxiety adorned it. Kaelix didn’t know what to do; all he could do was gingerly smile.

“How…could you? Why didn’t you tell us your mana was out?!” Zeal’s raised voice made Kaelix flinch, but he knew it wasn’t out of anger.

“I was trying to warn you, but before I could, I passed out,” Kaelix said plainly.

“You should’ve warned us 10 minutes before that point! Are you out of your mind?! You could’ve died!”

“We thought you were dead, Kae-chan.” Seible’s voice made Kaelix focus on the other two in the room.

Realization dawned on him as he saw his teammates all battered and bruised, with bandages and casts on them. Freo had a cast on his leg and bandages on his shoulder, Seible had wrappings around his head, and his fingers were taped together. Zeal was the worst, without a shirt on, his entire torso was wrapped tightly in bandages, and his left arm was in a sling.

“You need to learn self-preservation. If we hadn’t gotten out of there when we did, all of us would be dead.” Freo’s deadpanned voice, coupled with the harsh truth, made Kaelix tear up.

“I can heal you now, my mana feels fine.” Kaelix lifted his hands, but Zeal grabbed them.

“Don’t you dare.” Zeal’s voice trembled as he held back tears. “I don’t want to lose you, Kaelix. Don’t do something like that again.”

Seeing Zeal on the verge of tears made something break within Kaelix, tears spilled out from him as he began sobbing. His wails were quiet but desperate as he held out his arms, and the others looked at each other before moving to embrace the youngest. Soft weeps rang out from the otherwise silent room.

“We need you here. Don’t forget that.” Freo’s voice was restrained as tears ran down his face.

“I’m sorry…I’m so, so sorry. I won’t do it again, I’ll make sure I have enough mana so you guys won’t get hurt. I’ll take care of myself better, I promise.” Kaelix’s muffled ramblings only made his sobbing worse.
When they all calmed down, Kaelix lay back down, his eyes heavy with sleep, but not wanting to close his eyes. Zeal grabbed his hand tenderly and gave a small smile.

“Go to sleep, you need to recover.”

Kaelix tried to speak, but Freo just shook his head. “Get some rest, we’ll all be here when you wake up.

Seible smiled brightly and nodded in agreement. Kaelix chuckled and squeezed Zeal’s hand.

“I promise I won’t leave your side. So promise you won’t leave mine.” His voice deepened as sleep began to overtake him.

“We promise.” The other three spoke in unison, enough to reassure Kaelix as he drifted to sleep.

Zeal placed his forehead on Kaelix’s hand, “We’ll protect you until the end of time.”

Determination filled his voice as he made the promise; failure was not an option. Not again.