Yoriichi and Hiru didn't speak for long, but from Hiru's tightly knit brows and the way he followed behind him with his arms crossed, it was clear he'd been persuaded.
Uzui had meant to say something, but the lingering chill at the back of his neck hadn't fully faded. In the end, they only exchanged a brief nod and left it at that.
After the twins finished sparring with Tanjiro, Yoriichi stepped in as well. Unlike the restraint he had shown earlier—
Facing him, Tanjiro slipped completely into a demonized state. Yet no matter how fast or vicious his bone spikes lashed out, they couldn't even graze his clothing.
It wasn't until Tanjiro was on the verge of losing himself—just like on the Infinity Train, when he tried to abandon him and attack Hiru—that Yoriichi struck the back of his head with the sword's hilt, snapping him back to his senses.
Afterward, when Tanjiro and the twins asked questions, he remained as patient as ever. He carefully explained how to control the Slayer Mark and the Transparent World, as well as how to use Breathing Styles to keep the mind clear.
As Tanjiro began to grasp it, Uzui also picked up quite a bit about both by listening in.
"So the Slayer Mark is pretty useful, huh?" Uzui raised a brow. "A huge boost to physical ability—sounds flashy."
But Yoriichi gave a slight shake of his head.
"Once it's activated, it's hard to turn off. For ordinary people, it burns through their life. Those who awaken it rarely live past fifty."
"Then what about Tanjiro?" Muichiro grabbed his sleeve. "He's already awakened it. Once he turns human again, doesn't that mean he won't live long?"
"I'll be fine," Tanjiro said with a smile. "Sensei has already taught me how to control it. As long as I'm careful after turning back, there won't be any problems."
"Mm. It requires constant vigilance, but it's the only way to extend your lifespan," Yoriichi said, looking at him. "Demons are different from humans. Even if they push their bodies too far, their regeneration offsets the strain. If possible, you should return to being human before taking the medicine."
"Yes, I'll do my best! But…" Tanjiro hesitated, pressing his lips together. "Sensei, were you the same back then? I mean… did it also put that kind of strain on your body?"
"No. I was born this way," Yoriichi replied, shaking his head. "More precisely, it was only after becoming a demon that I unraveled its secrets—and finally saw the world as ordinary people do."
"But I've remained in that state for so long that, even now, normal vision and it still overlap. If you can't shut it down the way I described, have your Kasugai Crow send word to me. Once I'm done with what I need to do, I'll come teach you."
Hearing this, Muichiro felt both relieved and thoughtful—but soon, confusion crept back in.
From his explanation, it let you see muscles and bones, yet it wasn't a change in vision. It was more like losing control over your own perception. More than that, it wasn't a boost at all—it was a condition.
In other words, although he had explained it to the twins, he had no intention of encouraging them to pursue a power that came at the cost of their own bodies.
No matter how Muichiro thought about it, he couldn't understand why anyone would chase something like that. Even if, as Tanjiro said, it greatly increased combat strength, that kind of "vision" sounded extremely uncomfortable.
[Still… if I ever get the chance, I really want to try it. The "pinnacle of martial arts" just sounds so cool!]
Yuichiro only needed one glance at his eager expression to know exactly what his brother was thinking. But aside from a helpless sigh, there was nothing he could do—because, truthfully, he felt a bit curious himself.
Even so, Yuichiro decided to follow his advice and keep both himself and Muichiro away from it. There might be ways to shut it off, but better safe than sorry.
If they learned it only to find they couldn't turn it off later, that would be a disaster.
Not to mention, aside from him, the only known user—Tanjiro—was an F… ahem, someone with absolutely no teaching ability.
Yuichiro didn't mind for himself, but he didn't want Muichiro to end up in that situation.
[…Still, if something dangerous really happened, Muichiro would probably grasp it faster than me, right?]
Yuichiro frowned slightly.
[In that case… should I learn it first, just in case?]
The twins were each lost in their own thoughts. Hiru, still affected by the earlier conversation, stood off to the side with a frown, ignoring everyone.
Uzui, however, didn't expect Yoriichi to approach him after giving Tanjiro a few final instructions.
"I'll have to trouble you to watch over Hiru for now."
"Don't put it like that. I know my limits. In the worst case, all I can do is pass along a message," Uzui said, glancing at him as he rubbed the back of his neck. "What about you? Still planning to keep searching for the Infinity Castle?"
Yoriichi didn't answer right away. Instead, he turned to look at Hiru, who still stood there with his arms crossed, clearly displeased.
After a brief silence, he spoke.
"…No. I'm going to deal with what I've set in motion."
Uzui raised a brow. "Something to do with your brother?"
"Mm." Yoriichi nodded lightly. "As the elder brother, I can't keep leaving all the decisions to Hiru. And… there are things I need to say to him."
"In any case, I'll leave Hiru to you. And thank you for earlier, at the meeting."
[So it's come to brothers turning on each other…]
Uzui glanced at Hiru, whose expression remained tight and troubled.
"…Got it. But there's no need to talk like that, is there? Don't tell me you can't handle him."
Yoriichi froze slightly at those words. He lifted his left hand, instinctively reaching for his sword hilt—only to grasp empty air.
The motion stalled. After a long pause, he spoke again.
"No. My brother isn't as strong as I am… I…"
"I know, I know…" Uzui watched him clench his fists, then let out a long breath. "I've been through brothers turning on each other too. I know what that feels like."
Yoriichi looked up. "Uzui… you know?"
"Yes. Back when I was still in the clan. Shinobi training was brutal. The nine of us were raised separately by our father, and in the end, without even realizing it, we were made to fight and kill each other," Uzui said, a faint frown forming.
"By the time I understood what was happening, only me and a half-brother were left. Thinking about it… aside from mission targets, I probably killed five of them."
"After that, I left because I couldn't accept it. But that younger brother of mine kept hunting me down. In the end, I let him go every time."
"He's already become nothing more than a tool—beyond saving. But if I killed him, I'd be dragged back to become that disgusting clan head. So keeping him alive works just fine."
He paused, then added more quietly,
"Honestly… growing up in a family like that, I envy you two. Trusting each other. Supporting each other. When I said I wanted to be your younger brother—I wasn't entirely joking."
Yoriichi opened his mouth, but no words came.
Uzui's expression, however, remained steady.
"If you can't bring yourself to do it, then think about why you have to. No matter what happens, there will always be things you don't want to do—but have no choice."