Chapter Text
"It's good to see you again," Muzan said, subtly approaching, his gaze fixed on those two blue irises.
There it was.
Those two immense pupils that widened with every glance, every time they saw each other. It was starting to feel ridiculous, the number of times he found himself feeling the same thing, over and over, that surge of repressed emotions trying to break through the surface whenever he saw the demon.
"I'll kill you," Zenitsu whispered heavily.
The injuries inflicted by the king's subordinates had been endless, all of them attacking with a single purpose: to bring him to the center, to the meeting point with their miserable king, who was now carefully observing every sign of pain on Zenitsu's body without a hint of remorse.
"You fell in love, didn't you?" he heard in his head, his master's words, with that smug grin as if he wouldn't judge the answer.
He never replied. And if he could now, he'd rather cut out his own tongue than admit to feeling anything for the monster in front of him.
Muzan gracefully observed Zenitsu's ridiculous posture. Anguish and weakness were pouring out of him. The blood in his body pulsed with the survival instincts forged in battles he never should have fought. That wasn't the plan, after all. They had arrived at the Infinity Castle, or as he called it, the pinnacle of his legacy. Zenitsu shouldn't have been there; he was supposed to be safe at the Master's Estate, where he was meant to wait for the demon and everything would begin.
After all, they still believed he would be Muzan's perfect weakness. It was partially true, because Muzan had arrived with the thrill of war, with spine-chilling laughter as he effortlessly slaughtered the master's family in seconds. Zenitsu had heard everything, locked in the courtyard with the moon above, the lights reflecting the little innocence he had left. The heartbeats were slowly fading, and Zenitsu couldn't do anything. Not when he sensed it, not when he knew he wouldn't do it. He still couldn't cut off his head; he still couldn't wield his Nichirin against the crueliest demon of all. Not when he still felt his presence next to him all the time, overshadowing his light, taking him away from all that was good.
He should have never agreed to be part of that mission so long ago. He should have known, everything always went wrong for him in some way, and the monster deciding to obsess over him was not part of the plan.
He still remembered that fortune teller who judged Tanjiro with her eyes as she read his stack of selected cards in her dark tent, lit only by candles. This was about two years ago, when they had finished a mission assigned by the crows near a clandestine witchcraft fair in the closest village. The boys were tired, a little depressed. There were no smiles that afternoon, no sweet feelings, just waiting and patience. Zenitsu hadn't wanted to participate, but Inosuke's insistence on knowing what awaited him was stronger. Finally, he sat in front of the woman who laughed with a certain glee upon seeing him tremble in fear when she offered one of her cups. It contained a strange, colorful liquid that didn't seem to taste good. And when he finally drank from it and the foul-tasting herb ashes remained, Zenitsu knew something had changed.
The woman only smiled with more grace before sharing his future: "The only thing I see is a dark shadow clinging to you; nothing seems to pull it away, nothing and no one."
Zenitsu came out of the shadows, hitting Inosuke's arm in annoyance, without sensing a demonic presence between them. Tanjiro was the only one who felt it. It had been him, Muzan, and the rest was history.
Returning to reality, Muzan was muttering some words. Zenitsu didn't understand him that well; sometimes the demon spoke another language, aware that no one but him could understand it. It was incredible, sometimes even a little alluring when he did it. Like when they met after hours of a turbulent mission that left Zenitsu with fractured ribs and blood on his head. Muzan would silently appear next to him, taking him away while Zenitsu mentally debated whether to scream or break free because it was complicated. It would always be complicated between them.
Zenitsu sighed audibly. "First Form: Thunderclap and Flash!"
A single blink was all it took for Zenitsu's aura to become a golden bolt of lightning. His body, moved by instinct and years of practice, lunged toward Muzan at a speed that distorted the space around him. It wasn't just an attack, it was an art: the sound of his sword cutting through the air was a sharp crack, the smell of ozone that always accompanied his breathing and his nichirin, a familiar scent only he could summon. The cut almost reached the demon, who didn't retreat but instead drew closer, almost as if he were attracted, like a moth to a light, ironically, as Zenitsu thought he was. Muzan muttered something else before a visible flash was launched, but it caused no pain. He never hurt him; he played, but without causing harm. Zenitsu was mentally grateful for that, but now he wished he would, just to have another excuse to do it. Everyone trusted him to do it.
Muzan's attacks, in contrast, were a macabre and elegant dance. His long arms, mutated into whips of flesh and blood, moved with lethal grace. They didn't seek to injure, but to deflect. Every strike Zenitsu threw was intercepted not by a hand, but by a limb that would instantly deform and retract, like a river of dark matter moving at his will. It was a perfect defense, a way of mocking Zenitsu's strength without harming him, playing with his prey without giving him a chance to escape.
The fight continued with hard-hitting attempts to cause damage, all completely avoided or regenerated. Muzan did nothing; he just held his position, watching all of Zenitsu's movements intently, without fear or a desire to act. In his eyes, Zenitsu only saw tranquility, a sense of relief, as if simply seeing him in front of him was enough for a moment's peace. He was probably hiding from one of the pillars. Zenitsu had heard one of the crows shouting strategic positions. He was about to head to one of them, but the distraction, the sense in his body that said "help, fight," was calmed by the swarm of clumsy demons running toward him. The idea of supporting his own kind faded into the background as he failed to realize it was a trap to get him alone with his monster.
Zenitsu kept attacking, his sword echoing like a clap of thunder in the vastness of the castle. From one form to another, his body moved with a precision that only years of experience could grant. He was no longer a mere demon slayer; he was an extension of the storm, his breathing a motor that allowed him to dodge Muzan's defensive attacks with unmatched agility. He launched clean, direct cuts to the head and neck, the demons' weak points, but Muzan, with that disturbing familiarity, simply twisted his body or moved a limb to deflect the blade's edge. It was as if he knew exactly what Zenitsu was going to do before he did it.
Muzan advanced little by little. Eventually, Zenitsu debated whether to continue fighting a meaningless battle. At one point, as Zenitsu was thinking about other forms, he knew he had hesitated for too long. He turned, and his Nichirin blade was a centimeter from the demon's neck, at a very short distance.
For the first time in history, a living being had grazed the demon king with a Nichirin.
Muzan didn't flinch. He just smiled.
“Hello, my love.”
Zenitsu knew he had to continue. He put all his strength into his hands. His fists were starting to hurt from how tightly he was holding the hilt. He knew his fatigue was setting in when his heart began to slow its rhythm. His breathing became labored, the room started to spin, all the pain. He clearly heard the sound of that Upper Moon demon's instrument, who dared to have the power to rotate the entire Infinity Castle at her whim. He knew that changes were happening every second, but for the first time, he felt truly dizzy. Muzan still didn't flinch; he even seemed to have pressed himself harder against the blade, breaking a bit of his regenerative skin, and a glimmer of dark blood fell onto the floorboards beneath them.
Zenitsu could almost hear the many conversations behind his back about how he wouldn't be able to do it, and he was starting to believe they were right. He had the demon king on his sword; he could simply move it further in. He wouldn't die, he was sure of that, but they would be giving up valuable seconds for the other pillars to arrive and finish him off. But his body wouldn't cooperate, his survival flutter wasn't there. His friends would be disappointed.
He couldn't. He didn't want to do it.
"I couldn't either," Muzan confessed, with that beautiful baritone that few could hear. "It's not natural to kill what you love most, Zenitsu."
The mentioned looked into his eyes with glimmers of anger.
"I won't talk to you."
"I understand," the demon accepted. "But I just wanted to see you before this massacre continues. You're going to lose, Zenitsu; you're on the wrong side."
"I'm not, you're the one who will lose."
Muzan smiled. "Really? Then why isn't there another Pillar here besides you? I lured you to me, Zenitsu. If I hadn't, you wouldn't be this close to achieving what you planned to do. Your gaze says a lot, but it's your gestures that betray you. You can't and you don't want to kill me."
Zenitsu hated how right he seemed to be. Eternal seconds passed where they both looked at each other with precision. One with anger, the other with calm, patiently waiting for a change. There were no external noises; it seemed the room they were in was isolated with soundproof walls that allowed no sounds of battle or dying screams. He saw himself in Muzan's eyes, dying as he watched his companions perish before such power under a monster.
"Come with me."
It wasn't a command, or a question. It was a request, almost a plea.
Zenitsu couldn't believe the way he had said it. Finally, with heaviness and weakness, he let go of the sword, which resonated loudly between them as it hit the wood. Zenitsu, dazed, looked anxiously at the two reddish irises that only revealed indifference, but with many layers of kindness if you looked closely. It almost seemed like he felt pity for Zenitsu. He took a moment to respond. By instinct, he tried to retrieve his Nichirin, but was abruptly stopped by Muzan's arms that wrapped around him before lifting him into the air, moving far away from there. Zenitsu, without strength, without any intention, allowed the movement while leaning on Muzan's broad chest as he moved quickly through that infinite labyrinth.
Zenitsu could almost hear the voices of his acquaintances, friends, and companions. He tried with a vague effort to break free, but the strong, possessive grip was too much to even try, and he stayed still. The lights of everything caused many headaches, but the view was beautiful. So many Japanese buildings and rooms really impacted a simple human being. Muzan didn't stop for anything and wasn't seen. It wasn't the first time he had traveled with him, but it would undoubtedly be the most terrifying.
They arrived at a clearing in the middle of the main floors. Many doors were opened, others closed, the walls rotated. Zenitsu had no idea how to get home or where Tanjiro and Inosuke were. He was deposited with care on the ground where he could only observe the ceiling surrounding the base, as dark as the night itself. He didn't feel the hands coming towards him, wrapping around his body as Muzan moved away and gave orders with his sharp kingly voice until he approached, moving the many hands away from his face and crouching down beside him.
"Wait for me here; we'll be eternal together, you and I."
Zenitsu waited.