What kind of person… was Kaigaku, really?
When he was still an orphan, even when survival meant drinking muddy water, he never thought it unacceptable. To him, it didn't matter what he had to do—so long as he lived, he believed he could eventually change his fate.
When he was taken in by Gyomei Himejima, he behaved no differently from the other children. He laughed, he ate with them, and when Gyomei gently patted his head, he would even smile with genuine happiness.
But everything changed the moment his life was threatened.
After stealing money, he was cast out of the temple in the dead of night. Faced with death, he didn't hesitate. He extinguished the wisteria incense that protected the temple and pushed his former companions into the jaws of the demon in his place.
Even Gyomei—the man who had taken him in—was among them.
After leaving the temple, driven by a desire to grow stronger, the still-young Kaigaku traveled a great distance to Mount Momoyama, where he became the disciple of Jigoro Kuwajima, the former Thunder Hashira.
There, he trained relentlessly, pouring everything into his growth, and it wasn't long before he earned his teacher's recognition.
In time, he joined the Demon Slayer Corps. Though he wasn't well-liked, he continued to climb step by step, hunting demons and sharpening his skills, just like countless others who dreamed of one day becoming a Hashira.
And he came close.
But during a mission—at the very brink of that future—he encountered Kokushibo, Upper Rank One.
Alone. Helpless. Facing an overwhelming power far beyond his reach.
He resisted, at first. But soon realized the truth—he couldn't win.
So, in order to survive… in order to become even stronger…
He yielded.
Under Kokushibo's coercion, Kaigaku chose to become a demon.
He never once stopped to consider what his transformation would mean for others.
Even when Jigoro Kuwajima, his teacher, committed seppuku to atone for his failure…
Even when Zenitsu Agatsuma confronted him, demanding answers…
Kaigaku remained unmoved.
He felt no guilt. No sorrow. No remorse.
To him, none of it had anything to do with him.
He didn't grieve for his teacher's death. He didn't regret his choices. He ignored the scorn of others entirely. Instead, he felt only anger—anger that despite all his efforts, his teacher had still chosen to pass on his legacy to someone like Zenitsu, whom Kaigaku considered nothing more than a useless coward.
Later, when the two of them finally clashed—
Kaigaku, who could not use the First Form, faced Zenitsu, who had mastered only that single technique.
And yet, Zenitsu unveiled something new.
Thunder Breathing, Seventh Form: Honoikazuchi no Kami (Flaming Thunder God).
A technique Kaigaku had never seen before.
A technique that defeated him.
Even then, Kaigaku didn't accept it.
He didn't see it as his own failure. Instead, he believed it was simply favoritism—that their teacher had taught Zenitsu something he had withheld from him.
Even when Zenitsu explained that the Seventh Form was his own creation… a technique he had developed for the sole purpose of one day fighting alongside Kaigaku…
Kaigaku felt nothing.
No gratitude. No understanding.
Only anger.
Anger that someone he had always looked down on could surpass him.
And even in death, he never once believed he was in the wrong.
At the very end, reduced to nothing but a severed head, he was mocked by Yushiro:
"A man who never gives to others, who lets his desires grow unchecked, will end with nothing… dying alone. How pitiful."
So what kind of person was Kaigaku?
To Soma, the answer was simple.
An extremely self-centered man.
Even selfish, to the core.
And someone like that… would almost never find companions willing to entrust their lives to him.
And yet, Soma still chose to say those words—to speak of a team that would be willing to guard his back, even sacrifice for him.
To Kaigaku, hearing that wasn't something to question.
It simply made him feel… pleased.
He would never stop to wonder whether someone like him—so utterly self-focused—could truly deserve such companions.
So Soma gave him another, unspoken question:
Are you worthy of it?
Most people, when faced with that question, would hesitate.
If you would not risk your life to protect another's back, then why would anyone protect yours?
But Kaigaku was different.
In his mind, the answer was simple.
If he wasn't worthy now… then it was only because he wasn't strong enough yet.
And once he reached a certain height—
Once his strength was undeniable—
Then having others sacrifice for him… would only be natural.
But all of that had one condition—
He had to be strong enough.
And that… was the path Soma had laid out for Kaigaku.
By all logic, someone like Kaigaku didn't deserve teammates.
Yet at the same time, someone with his potential—someone capable of reaching great heights through sheer ability—was he really someone to be discarded so easily?
At least in Soma's eyes, the answer was no.
A person like that still held immense value. In fact, when it came to slaying demons, someone like Kaigaku might even perform better than most.
Soma's way of thinking was simple.
As long as a person could be useful—could contribute, could accomplish things—and truly had the ability to back it up, then flaws in their personality, no matter how glaring, could be tolerated.
After all, if you wished to make use of someone's strengths, you had to be willing to accept their weaknesses.
No one in this world was perfect.
And what Soma wanted… was never complicated.
All he sought was to kill Kibutsuji Muzan.
People like Kaigaku were nothing more than pieces—useful ones—helping to build toward that goal.
So when he looked at Kaigaku, who had unconsciously tightened his grip on his sword and declared, "I'll make you believe that I am worthy," Soma simply reached out and patted his shoulder.
His tone remained gentle.
"Whether you're worthy or not isn't for me to decide," he said. "That's something your companions will judge. But right now… they don't accept you. In fact, many of them have a problem with you."
Kaigaku lowered his head silently. Of course he had noticed the looks—those strange, distant gazes from the others.
He just didn't care.
"I can see your potential," Soma continued. "In fact, I think that one day, you might even become a powerful Hashira. But in their eyes… that may not be the case."
He gave a slight shrug.
"They might even think that someone like you—someone unfit to have companions—won't survive long before dying at a demon's hands."
Kaigaku clenched his teeth.
Soma said nothing more. He simply gave his shoulder another light pat before turning and walking back toward the campfire, rejoining the others as if nothing had happened.
With his strength, his imposing presence, and his willingness to listen—along with the rare ability to lower himself and hear others out—the atmosphere around him quickly grew lively and relaxed.
Before long, people naturally began to gather around him.
…
Standing where he was, Nichirin Sword in hand, Kaigaku watched the scene unfold.
In his pale green eyes, there was something unmistakable—
Envy.
As time passed, the sun dipped below the horizon, and darkness gradually swallowed the land. Kaigaku lifted his head, staring at the dimming sky as his grip on his sword tightened once more.
He would prove himself.
He would show them his strength—his true ability—and force every doubt, every whisper of scorn, back down their throats.
Step by step, he would climb higher.
Become stronger.
Become a Hashira.
And when that day came, everyone who had ever doubted him—everyone who had said he was unworthy—would have no choice but to shut their mouths.
Perhaps it was that thought that lifted his spirits.
Holding his blade, Kaigaku walked toward the campfire. Even when he felt those lingering, uneasy gazes from others, he raised his head and gave a faint smile in return—his thick brows appearing even more pronounced under the deepening night.
…
Author's Note:
Originally, I hadn't planned to write a chapter focused on Kaigaku. I felt like I had already described him quite a bit. But seeing more and more discussion—and quite a few misunderstandings—I ended up adding this chapter at the last minute.
Writing about a character doesn't mean I'm trying to redeem them.
So why does everyone think I'm whitewashing him? It's honestly a bit frustrating…
I've been trying to stay faithful to the original characterization. The protagonist exists in a gray area between humans and demons—he didn't come to the Demon Slayer Corps to make friends. Whether Kaigaku is good or bad as a person doesn't really matter to him. Even if Kaigaku betrays the Corps, it has nothing to do with the protagonist.
It seems a lot of readers expect the protagonist to grow closer to the Demon Slayer side. But even earlier—like when he killed a Kakushi—some readers were uncomfortable, thinking it would create an unnecessary conflict with the Corps.
But there's no need to think that way.
Whether he kills or not, the outcome is the same in the eyes of the Demon Slayers.
There's only one demon they truly accept—Nezuko.
Or rather, they accept Tanjiro with Nezuko, not Nezuko as a demon.
Any other demon?
They're meant to be killed.
So how could a protagonist who is himself a demon truly trust the Demon Slayer Corps?
Aside from Kanao, who serves as a rare point of connection, everything the protagonist does is ultimately for himself.