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Tanjirou had been only nine years old when, curled up in his mother's lap, he reached a hand out to touch the mark on her cheek. There were no bumps or raised skin that made the mark feel different, it was as part of her skin as the mole on her chin. But this was nothing like a simple birthmark: it started on her jaw and grew upwards in the form of undulating flames, engraved in dark red—just like the color of his own eyes and that of his father.
With the innocent curiosity common to children, he patted the mark again and asked how his mother got it in the first place.
In that sweet and patient voice that his mother always had in his memories, she told him about soulmates for the first time.
"They're your special someone, Tanjirou," she said, tucking his hair behind his ear. "Be it a best friend or a lover, they'll stand by you until the very end."
"Oh," Tanjirou breathed, part wonder and part confusion. He blinked up at her. "Does the one on my shoulder mean the same thing? That someone will be precious to me like that?"
His mother's face then twisted into a sad smile, her brows furrowed. As soon as her expression changed, however, it was swiftly hidden from him once she leaned in to kiss Tanjirou's forehead.
"Yes, of course," she replied. "You're a wonderful child, I'm sure you'll find an equally wonderful soulmate."
His father, watching them silently from the other side of the room, had the same sad smile as his mother, and their scent was tinged with sorrow.
Tanjirou wouldn't understand why until years later, when he was old enough to reach his own conclusions on the possible implications of his soulmark.
Because Tanjirou was a child who, from the very moment he was born, had a mark that looked more like a vicious scar on his left shoulder, the exact same way one would have following the cruel bite of an animal.
***
It was supposed to be his own secret—or at least a family secret, unknown to their acquaintances and other friends. And yet the nature of his mark was a known fact to the entirety of the village at the base of the mountain.
He could hear them whisper sometimes when he came down to sell coal and chat with the locals; they were never cruel about it, quite the contrary, as Tanjirou was on good terms with all the villagers.
Maybe that was why they'd talk about it in such a sad, pitying tone, not all that different from how his own parents reacted whenever the topic of his soulmark was brought up.
"I just don't understand," the owner of the only restaurant in the village once said to one of the regulars. "Why would a bright child like that get such a scary soulmark? What kind of person will his soulmate be?"
"Who knows," the man she was talking to grumbled. "Fate is a mysterious thing."
"So I'm supposed to believe that something like this is fate?" The owner questioned hotly. "That someone like him is destined be with a b—"
"Enough," the man spoke over her. Then, quietly: "Don't speak of that anymore." Silence fell upon the group, and Tanjirou could no longer hear their voices.
The owner didn't need to finish for him to predict what she would say next. Tanjirou knew what they called him in hushed, horrified voices.
"The beast's soulmate".
***
It was on a cold winter day when he and Nezuko huddled close together, wide awake while all their siblings peacefully slept. There was a sense of foreboding that blanketed them both: Nezuko had woken up from a dream that she could not remember with a heavy heart, while Tanjirou had not slept at all, watching the darkness for hours on end as if waiting for something to come out of it.
Unsettled, they leaned on each other for support, hands clasped tightly together. For the first twenty minutes, their tongues were still, not daring to perturb the unnerving lull of the night. But soon they realized that the sun was in no hurry to come, and the clock handles dragged themselves to each new passing second.
They talked in whispers that only the two of them could hear, voices muffled under the blanket, words lost to the wind that roared outside and occasionally shook the wooden frame of the walls.
Conversation was easy, and the topics changed quickly as they went through whatever first came to mind, to keep themselves from thinking too much or too hard on what kept them up in the first place. They talked of breakfast, of chopping wood, of a bird feather found on the mountain path, of the sound of cracking of ice on a water surface they could hear when they came down the mountain to visit the village.
And when they both had gone quiet, at a loss for words, it was Nezuko who looked into his eyes as her smile fell from her face, a frown taking its place. She didn't look upset or angry, but serious and determined.
"When you meet your soulmate, they'll be wonderful. I know they will," she told him. "No matter what others say about it, you'll find someone wonderful."
Tanjirou had blinked at her, surprised at the sudden fire in her voice. "You don't need to comfort me, I'm not afraid."
"Yes, you are," Nezuko insisted. "Even dad made that sad face when any of us talked about soulmates in the room, everyone has always acted like that. But I know it'll be alright. Because I'll make sure they're good."
Tanjirou laughed and gently flicked her forehead. "If you say that, then I know it'll be okay." Pressing his forehead to hers, Tanjirou closed his eyes and sighed. "It's a promise, then."
"It's a promise," Nezuko confirmed.
They giggled between themselves, and hugged to seal the deal.
Tanjirou wasn't aware at the time, but that would be the last long conversation he would have with Nezuko before she was turned into a demon.
***
His throat burned, snow had melted and then frozen again on his clothes, it was hard to move or breathe or even think. The place where he was hit by the mysterious swordsman ached, he was sure there was a bruise forming there.
Tanjirou cried while he still could, hugging Nezuko's unconscious body as tight as his aching and trembling arms allowed him.
You promised me , he repeated in his head like a mantra as he struggled to get to his feet. You promised me, so don't give up yet.
***
He would've never imagined they would meet like this, both of them filled with adrenaline as they fought each other, though Tanjirou was more trying to appease the other than truly fight against him.
But when the mask falls, it is not the dissonance between body and face that Tanjirou notices, but the mark engraved on the boy's otherwise immaculate skin: two peaks growing on his jaw up to his cheek in jet black, with the circumference of the sun rising between them.
Tanjirou remembers looking at the same image, swaying gently where it hung from his father's earlobes; the exact one on the earrings that he now wore, clinging in his ears when he took a step back in shock.
For a moment, Tanjirou thought he might have been punched in the stomach, as it's suddenly hard to breathe. Though it takes only a second to realizes he's fine, that does nothing to alleviate the buzzing in his skin, a sort of overwhelming giddiness so overpowering it hurts, like he'll get split in two from the emotion alone.
He couldn't think, couldn't see anything else but him, even somehow saying something about how attractive the boy's face was. Then, worry substituted wonder.
"Sit down, are you okay?" He says, stopping himself from checking, from touching his soulmate's face to evaluate his injuries.
And when the boy fell, Tanjirou hurried to pillow his head—even if it didn't help much in regards to undoing the damage, at least it would make the position less uncomfortable.
As Tanjirou pulled back, his hand lingered on the pale cheek, brushing tip of the mountain there.
Hashibira Inosuke.
I found you.
***
The ambiguous time of the night when it was not yet late, but simultaneously no longer early had Tanjirou sitting alone outside their shared room in the House of Wisteria. The moon was shining in full, but Tanjirou looked at it without really seeing it.
The warm breeze ruffled his hair, and Tanjirou closed his eyes to appreciate it, just as soft footsteps sounded somewhere behind him.
Tanjirou didn't have to look to know that it was Zenitsu who watched him, emanating worry and uncertainty.
He thought he might not speak at all, but soon his voice joined in with the cries of the cicada.
"It's him, isn't it?" Zenitsu asked. "Your soulmate."
Tanjirou thought of green eyes and rosy cheeks, of a boy who was sometimes more beast than human. "Probably."
"What are you gonna do about it, then?"
Tanjirou smiled and tilted his head to the side, seeing the leaves on top of the trees shuffle about at the corner of his eyes. "Nothing." He clenched his empty fists. "I'm not doing anything."
***
"Tch, that's one inconvenient soulmark you've got there," Uzui complained as he continued to pat more and more makeup on to Inosuke's face.
Inosuke, already angry from being manhandled like a doll, growled deep in his throat. "What the hell is a soulmark?"
Uzui paused, staring at Inosuke in disbelief. "Are you shitting me? You've got it right there on your face, you do know that, right?"
Inosuke raised a hand to his own face, though his expression had question marks written all over it.
"Huh?"
Uzui sighed to himself and grumbled something that sounded suspiciously like "these goddamn stupid brats", but who knows, Tanjirou wasn't the one with sharp hearing.
And even if he was, Tanjirou was too busy trying to sink into the floor to pay attention to what Uzui was saying. Sat in perfect seiza , he stared at his own knees as the conversation washed over him. Zenitsu was growing increasingly frantic as he glanced between Tanjirou and Inosuke.
In his current state, most of Uzui's explanation of what a soulmark is didn't really make it into Tanjirou's ear. The situation made him feel suddenly wrong-footed, like the floor had disappeared under him. Tanjirou only looked up when a concerned Nezuko placed her hand on his shoulder, and he hurried to let her know he was fine by smiling at her.
"...they're supposed to be your other half, stuff like that. Someone who supports you and makes you stronger that way," Uzui was just finishing saying to a scowling Inosuke.
"I don't have something like that!" Inosuke protested angrily. "I don't need it, I'm already strong on my own!"
Tanjirou froze, and Nezuko tugged more insistently on his sleeve. Even Uzui (more perceptive than they gave him credit for) had paused to look back at him, and even if they were just trying to help, but Tanjirou just couldn't take their sorrowful gaze.
"I'm fine," he told Nezuko, not making eye contact with anyone else. "Don't worry about it."
There was a second of awkward silence, but soon enough Uzui started going on about the details of their upcoming mission, and the subject was dropped.
***
Some days were bad, but others were worse.
Too often, Tanjirou would turn as he thought he heard the crunch of leaves, or smelled the scent of pine trees and wet soil. More rarely, he would start walking without thinking much of it, only for a put off Zenitsu to remind him they were supposed to go the opposite direction.
On top of it all, it felt like Tanjirou rarely slept lately, as even when he did, it was restless, with dreams waking him up in the middle of the night. The dreams were too jumbled up to make sense of, and always faded away the moment Tanjirou grew more alert. The only thing left would be the tug at the base of his stomach, and a bout of paralyzing dread.
But once that faded as well, with the silence as Tanjirou's only company, his hands felt all too empty, heart far away however many miles down the road where Inosuke was.
Tanjirou couldn't do much more than cover his eyes and breathe in slowly, wondering when he had started falling this hard.
***
Seeing Inosuke again felt the exact same as coming home after a long trip: it relaxed his body, brought a sense of relief, and happiness that the waiting was over and now just fuzzy contentment was present. Just like one would collapse on their bed after an exhausting day, Tanjirou fell into Inosuke's arm with great desperation and no finesse. They collide and tumble in a heap of muscles, and only Inosuke's strength keeps them from an ugly encounter with the ground.
Inosuke tugs at his hair, but never really pulls away, settling for making disgruntled questions in that growling voice of his. Tanjirou almost laughs at himself when he thinks of it as endearing, but something inside himself is starting to crumble at the edges, the points where Inosuke touches him, just like an old painted wall being picked at to reveal the layers underneath—which were never meant to be seen in the first.
It's the fear and insecurity stills his tongue, but not his body: Tanjirou hugs him to his chest like they haven't seen each other in years, with all of the longing of various sleepless night behind it. He might shake a bit when he works his fingers under Inosuke's mask to grasp at his hair, but Tanjirou can't quite tell anymore, too out of himself with emotions that he's growing tired of carrying.
"You're acting weird," Inosuke complains loudly, but he has his hand on Tanjirou's back in a loose embrace. "Did you hit your head or something?"
"No, I'm all good, really," Tanjirou reassured. To prove it, he pressed his forehead to Inosuke's gently. "See? As firm as always."
Inosuke, a bit miffed, scowled. "Then what's wrong with you?"
Tanjirou pulled away—not far, only enough to get a look at Inosuke, though the sight didn't reveal him anything, with Inosuke's mask hiding his expression. But Tanjirou himself had no such protection, face bare for all to see, and he wondered if Inosuke could see the fractures underneath.
"I'm just happy to see you're safe," Tanjirou told him, so terribly tender and affectionate as his heart bled into his words.
The sweet scent of Inosuke's happiness was enough to calm the bright red burn in his veins, to calm the roar into a hum, and he no longer felt the thread that pierced his skin and pulled him too far until his skin hurt.
It didn't go away completely, of course, but that night, sleeping next to each other with Tanjirou's hand outstretched between their beds (reaching but never touching), Tanjirou smiled and fell into a dreamless sleep.
***
It was only four days later when they were ambushed.
***
Tanjirou wanted to swing his sword violently, to put all of his rage behind each move, but that would only make him sloppy, so Tanjirou settled on biting the inside of his mouth until he tasted copper coating his tongue.
There was no time for reckless sentimentality: if he fell into despair, he would be of no use to anyone, and they couldn't afford that at the moment. Not when he needed to make sure everyone would make it out alive.
Not when he had to end the fight before Inosuke bled to death.
Blood that was not his own was still drying on both his hands, the smell a constant reminder of the minutes he spent holding a wound shut, hoping that would be enough to prevent the worst. He hadn't wanted to leave Inosuke's side, but with battles still going all around them, he only put them in more danger by staying idle.
Tanjirou could only hope that hiding Inosuke where the bushes grew the tallest, and wrapping his wound with Tanjirou's own haori would grant him safety until Tanjirou could make his way back to Inosuke.
That was all he thought of, even when he could barely see from one eye due to the blood dripping into it from his forehead, even with what was possibly a broken arm.
Even when the demon in front of him disappears with a final whisper: "He'll take everything from you…"
His heart feels frozen, but too fast at the same time. Tanjirou stumbles forward, walking straight into someone, and he looks at Giyuu's frowning face. There's a grimness to him that Tanjirou can't quite understand.
"I need to find him," Tanjirou tells him, trying to step around Giyuu. "Inosuke… I have to make sure he's safe."
"Tanjirou."
"I can't smell him, there are too many smells, I can't tell if he's okay," Tanjirou rambled, aware that he was slipping into delirium. "Giyuu-san, I have to find him…"
Giyuu held him back with a hand, and Tanjirou tried to struggle out of the grip, but that only made Giyuu tighten his hold on him.
"Tanjirou, listen to me," Giyuu urged, shaking him by the shoulders. "He's gone."
Tanjirou blinked up at him. "...What?"
"I went after him, he isn't there."
"The bushes—"
"I checked them," Giyuu said in a hard voice. His jaw clenched, he looked to the side, his grip so stiff Tanjirou feared he might break under it. "I checked everywhere, he's not there. Inosuke's body is gone."
***
He would've expected to feel something more… earth shattering. In fact, he's sure he should be feeling something. Instead, Tanjirou finds himself smiling when someone asks him a question, the motion automatic but not forced.
He developed a tendency to zone out, unaware of his surroundings until someone would wave a hand in front of his face, and at that point Tanjirou would have to ask if they had said something. It never failed to get him concerned looks, but Tanjirou couldn't feel the weight of that, either.
Cooped up in the Butterfly Estate, Tanjirou had a routine, which he went through like clockwork. However, the only parts that stuck out in his mind where the moment when he would join others to eat, the voices breaking him out of the stupor he spent the rest of the day in, wandering around the house and sometimes even outside. And if someone asked him where he was going, Tanjirou never had an answer.
It was in one of those moments that Zenitsu had found him back in the patients' room, sitting on one of the beds. When he came in, Tanjirou looked up with a serene smile.
Zenitsu shuffled about, hesitant to even take a step forward—Tanjirou thought he ought to ask for his friend's wellbeing, but his tongue never moved, his mouth never opened.
Absentmindedly, Tanjirou rubbed his left shoulder: the one that had his soulmark, the one that had gone numb the night of Inosuke's disappearance. If he tried to move it, Tanjirou felt needles working themselves deeper into his skin.
"I wonder if this is what it feels like," Tanjirou mused out loud. "To lose a soulmate, that is."
There was a sharp intake of breath, a pause, then quickly approaching footsteps. Tanjirou looked up, but as he did so, a hand connected with his cheek, turning his head to the side.
With wide eyes, Tanjirou raised a hand to touch the side of his face, where the skin was hot. He looked at Zenitsu from the corner of his eyes, finding him fuming with his fist closed tightly by his side, like he was refraining from slapping Tanjirou again.
"Get ahold of yourself!" Zenitsu shouted. "What are you doing, walking around like you're a ghost or something?! You won't even look at Nezuko-chan anymore! Do you have any idea how worried she is?"
Tanjirou choked on his next breath, but held in the cough that rose in his throat.
"You've just been standing there, not doing anything. What about curing Nezuko-chan? And finding Inosuke? This isn't like you at all!" Even if Zenitsu's voice was harsh, there was an underlying desperation to his tone that Tanjirou picked up on. "If you don't snap out of it, I'll—"
Zenitsu broke himself off, breathing harshly and shaking where he stood. Tanjirou tried to reach for him, but stopped midway.
"I'll hit you again, you know!" Zenitsu cried, and there were tears streaming down his face. Tanjirou felt his own heart pound heavily and his eyes sting.
"...I'm sorry," Tanjirou whispered, because the lump in his throat wouldn't let him speak any louder than that. "I'm sorry."
Zenitsu threw himself at him, and Tanjirou clutched at him, holding on as he drowned in a wave of his own grief, sobs ripped out of his him.
Tanjirou cried as all he smelled was the sickening scent of blood.
***
"You know he won't be the same when you find him," Shinobu said carefully, while Tanjirou made preparations to leave.
"Neither was Nezuko," Tanjirou countered.
"But not all demons are like your sister," Shinobu reminded him.
"There were many humans in the woods that night, if Inosuke really turned into a demon, he left without attacking anyone." Tanjirou had reflected on the subject many times before reaching this conclusion, and by now he could say it with confidence, set on the fact that Inosuke wouldn't have eaten any humans. "Besides, Inosuke is stronger than anyone I've met. I trust him."
Shinobu tilted her head. "Even now?"
"Even now."
Shinobu smiled and nodded approvingly. "Good. Then, do your best."
"I will, thank you," Tanjirou said, but got distracted by a tug on his sleeve. He looked down at Nezuko, and he felt guilty at seeing the concern in her frowning face. He would have to remember to do something nice for her later, to compensate for worrying her so much. "I'll be back soon, I promise."
He gave her one last hug before breathing in and turning on his heel.
"Tanjirou," Zenitsu called. Tanjirou paused, looking back at Zenitsu. "Bring him back," he said seriously.
"Of course," Tanjirou nodded. "You don't even need to ask.
***
Seeing Inosuke after days on end of traveling on foot guided only by instinct had been such a shock that Tanjirou thought he might be hallucinating, or dreaming.
As expected, there were changes to his appearances: his sclera was tinged deep black, with the irises changed from moss green to a lighter, more neon green that glowed under the moonlight. There were horns on his forehead, and sharp fangs so long they could be seen even when he had his mouth closed. His scent was different too, something more burning wood instead of falling leaves.
But there were things there remained the same, too, like the midnight blue of his billowing hair, or the pale complexion of his skin. And, more importantly, the mountains on his jaw.
Funnily enough, it wasn't the soulmark that made Tanjirou drop his sword. No, it was a simple strip of fabric tied around Inosuke's bicep, the familiar green and black checkered pattern easy to recognize. The one he had lost after tying it around Inosuke's injuries.
Before leaving, Tanjirou had asked Shinobu what happened to a demon when they saw their soulmate, to which Shinobu had given a morbid explanation of how the desire to be with their soulmate and the desire to eat humans overlapped and merged into the urge to consume the person in question. Tanjirou shivered just recalling it, and yet, he stood unarmed and spread his arms open in invitation.
When Inosuke charged at him, he didn't flinch, and when there were teeth sinking into his flesh, Tanjirou didn't fight to get away, though he cried out in pain.
"I'm here, Inosuke," Tanjirou said through gritted teeth. "I'm here. I'm with you. You're not alone."
He staggered back, legs losing strength, but Inosuke's hands on him kept Tanjirou from falling altogether. The pain spread from his neck down to his wrist, and his fingers twitched involuntarily.
"I'm here," he repeated. When Tanjirou pried one eye open, his vision swam. "I won't leave you, no matter what."
Inosuke growled, and his teeth dug deeper. Tanjirou felt his own blood drip down his shoulder and soak his clothes.
Tanjirou pressed his cheek to Inosuke's and panted, babbling incoherently as his consciousness faded.
***
He wakes to the sound of running water, and the sight of stars shining above him. His head feels fuzzy, and when he attempts to sit up, the sudden nausea brings him right back down.
No matter how much he breathes, his lungs still beg for air, so Tanjirou keeps inhaling deep, quick gulps of air.
"Inosuke…" Tanjirou croaks out, eyes roaming from side to side, searching for the familiar face. He keeps calling for him, stretching a hand out to pat the space beside himself.
Then, there's someone peering down at him and a hand clasping his own. Tanjirou looks up at Inosuke, who watches silently. When Tanjirou smiles fondly, he huffs irritatedly.
Directing his gaze to their joined hands, Tanjirou attempts to hold Inosuke's tighter, but he fails when he finds he has no strength in his limbs. Seeing his effort, Inosuke makes it so their fingers intertwine, his firm grip compensating for Tanjirou's slack one.
Tanjirou smiles again, and falls back asleep.