In the unwritten rules of the Demon Slayer Corps, if one's disciple were to fall and become a demon, the master must bear full responsibility.
But this was not merely a matter of responsibility.
For Jigoro Kuwajima, Kaigaku had once been his pride, the successor in whom he had placed his greatest hopes.
Even though the boy's personality was extreme and his ambition overly strong, Jigoro had always believed that through the tempering of the Thunder Breathing, somewhere behind that twisted pride there would remain a fragment of protective kindness.
"Old man..." Asuka opened his mouth, wanting to offer comfort, but realized he had nothing he could say.
The demon's corpse had already turned into drifting ashes that scattered through the mist.
Yet the silence in the courtyard was more suffocating than the battle that had taken place moments before.
"Asuka..."
Jigoro Kuwajima raised his head. His eyes were filled with the stillness of dead ash.
"You should go back. This old man... is a failure. There is nothing left I can teach you."
He lowered his gaze to his hands.
These hands had slain countless demons.
These hands had once gently wiped away the tears of young disciples.
These hands had sternly guided their grips on the sword.
"The successor of the Thunder Breathing has become one of the Twelve Kizuki... how terrifying... I raised a monster... I have brought shame upon the Thunder Breathing and dragged the honor of generations of Thunder Hashira into the mud..."
The old man slowly turned around and limped toward the interior of the dojo.
"This old man must go and fulfill... the final duty that remains."
Asuka followed him all the way to the doorway.
He watched Jigoro Kuwajima enter his tatami room and sit upright in the center.
The old man loosened his robe, revealing a chest covered with scars. Though aged, it remained powerfully built.
He picked up a piece of clean white cloth and slowly wiped the Nichirin Blade that had accompanied him for his entire life.
No explanation was necessary.
Asuka already understood the old man's decision.
Seppuku.
The most ancient and most brutal form of atonement.
It meant that he would walk alone toward the end of his life, enduring unimaginable pain.
"Won't you wait a little longer?" Asuka stood at the edge of the veranda, looking at the old man's profile. "The final battle is approaching. Perhaps you could end him with your own hands."
"No..." Jigoro Kuwajima's voice was calm, without a ripple.
"That is Zenitsu's task. As his master, the final answer I can give that traitor... is to wash away the filth he left upon this school with this old life of mine."
He paused, then suddenly turned his head and gave Asuka a faint smile of relief.
"Kid, thank you for letting me see that the Thunder Breathing... will not be completely severed."
"The other sword forms are recorded in the book of previous Thunder Hashira in my room. If you find them useful, take them."
"Go now. Don't look back."
Asuka stood there.
The old man's hand had already grasped the tip of the blade.
After a long silence, he bowed deeply toward the room.
"Thank you for your guidance, Master Kuwajima."
That night, the mist over Momoyama never cleared.
In the silent depths of that late autumn night, only a faint sound came from within the dojo — the quiet noise of a blade entering flesh, followed by the rustling of wind blowing fallen leaves.
Several days later.
The Ubuyashiki estate.
The atmosphere here had become tense to the extreme.
In preparation for the coming final battle, every Hashira and every ordinary corps member was undergoing nearly insane levels of training.
The courtyard was filled with figures drenched in sweat and the sharp clang of blades colliding.
Asuka stepped into the estate beneath the fading glow of the sunset.
Two swords hung at his waist, and his expression was calm to the point of coldness.
Anyone with a bit of strength could sense the change in him.
If before leaving he had been like an unpredictable gale, now a condensed and dangerous thunder pressure faintly circulated around him.
"Lord Storm Hashira! You've returned!"
Several corps members responsible for training nearby bowed respectfully.
Asuka nodded slightly and prepared to pass through the corridor to report his mission to the Master.
But suddenly, a yellow figure burst around the corner.
His movement was incredibly fast, accompanied by a rumble like thunder.
"Asuka—!!!"
A shrill roar filled with sobbing exploded through the corridor.
Asuka stopped walking.
Standing before him was the blond boy who was usually cowardly and terrified of death, always crying and whining — Zenitsu.
But Zenitsu now was different.
He did not rush forward to hug Asuka's leg and beg him to ease up the training like he usually would.
Zenitsu stared at Asuka with deadly intensity.
The eyes that usually carried constant anxiety were now bloodshot.
His entire body trembled violently, and in his hand he clutched a crumpled letter.
"You... you really went to Momoyama, didn't you?" Zenitsu's voice was hoarse, every word forced out through clenched teeth.
Asuka looked at him without answering.
"Say something, damn it!" Zenitsu stepped forward and grabbed Asuka by the collar. "Didn't you say you were going there to learn Thunder Breathing? Tell me! Were you really there?"
Asuka remained silent.
His gaze fell upon the letter in Zenitsu's hand.
That was the final letter Jigoro Kuwajima had sent through the Kasugai Crow on that night.
"You... did you watch him... watch him do that?"
Zenitsu's voice trembled with unmistakable sobbing.
His body nearly collapsed to the ground, yet he forced himself to stand.
"Tell me! They said the old man... for that traitor... for that damned bastard... he committed seppuku! And... and there wasn't even a second to end his suffering..."
"That was his choice," Asuka finally spoke.
His tone was as calm as ever.
Almost cold.
To Zenitsu, the words struck like a bolt from the sky.
"You were there... you were right there watching! Why didn't you stop him? Aren't you a Hashira? Aren't you supposed to be strong?!"
Tears burst from Zenitsu's eyes.
"He might have had a bad temper... he might have beaten me all the time... but he was my only family! He was the best old man in the whole world!
How could you... how could you just watch him die like that—!!!"
Anger and grief shattered his reason in an instant.
"You bastard—!!!"
Zenitsu suddenly swung his fist toward Asuka's calm face.
Bang!
Asuka neither dodged nor attempted to deflect the blow.
He accepted it head-on.
Because Zenitsu was consumed by overwhelming grief, the punch carried tremendous force. Asuka's face jerked sideways as the blow landed. The corner of his mouth split open immediately, a thin line of red blood seeping out.
"Lord Storm Hashira!!!"
The surrounding corps members were shocked and rushed forward to pull Zenitsu away.
Zenitsu had completely lost his strength.
He collapsed to his knees before Asuka, covering his face with both hands, letting out a wail like a wounded beast.
"Answer me... why won't you say anything..."
"Ugh... old man... Master..."
His crying drifted in the evening wind, echoing through the elegant yet cold corridors of the Ubuyashiki estate.
Asuka looked down at the boy kneeling at his feet.
He offered neither comfort nor explanation.
Instead, he removed the other Nichirin Blade from his waist and handed it to him along with a yellow-covered book from his robe.
"Go become stronger than anyone else. Don't look back."
Asuka stepped around the sobbing Zenitsu and walked forward.
"Old man, this is all I can do."
"Whether he will truly be reborn... is no longer something I can decide."
He murmured quietly to the air, touching the corner of his slightly swollen mouth.