After twenty-five days, Hiru finally returned to normal.
"Am I an idiot?!" Hiru covered his face. "How did I not leave myself any backup measures at all?! And seriously, what was with my brother's attitude?!
Why didn't he think about helping me solve the problem and instead looked like he was enjoying it?! If I hadn't already learned how to restrain myself when I was younger, I definitely would've ended up with some inexplicable black history!"
"But I thought that version of you was quite interesting," Yoriichi said, looking at Hiru with a gentle smile. "I missed that part of your life. Being able to see what you were like as a child makes me feel very fortunate. It's just a pity that I couldn't stay by your side more back then because of work…"
"Brother…"
"Hm?"
"…Where did you even learn to talk like that?" Hiru stared at Yoriichi intensely. "I already noticed it during the last Hashira meeting. Where did you pick up this way of speaking that people just can't deal with?"
"Hm?" Yoriichi froze for a moment, his expression softening even more. "I learned it from Uta."
"Huh? Sister-in-law?"
"Yes." Yoriichi nodded with a smile. "When I was practicing swordsmanship, Uta would sometimes use that tone to stop me and make me rest. Even though I never felt tired, seeing her like that made it impossible to refuse."
"Did you ever try to look for sister-in-law's reincarnation?"
Yoriichi shook his head slightly, his expression tinged with nostalgia.
"Even if reincarnation truly exists, that person would no longer be Uta, but someone else entirely. How could I treat her—or him—as a substitute for Uta? That would be disrespectful to anyone involved."
"That's true… but, brother…" Hiru sighed. "You really shouldn't use what she said on me."
"Hm? I made sure the grammar and wording were correct."
"That's not the issue! It's a matter of identity!" Hiru snapped. "I'm your brother—your younger brother!"
"…But it works very well, doesn't it?" Yoriichi said thoughtfully. "And Hiru's expressions really are quite interesting…"
"Brother!"
"Yes, yes, I understand. I'll be careful next time." Yoriichi laughed lightly. "So, have you figured anything out about that Blood Demon Art?"
"Somewhat…" Hiru tapped the palm-sized orange crystal on the table. "It can be confirmed as a curse-type Blood Demon Art."
"So your amnesia was actually your memories being sealed?"
"'Forgotten' would be more accurate than 'sealed.'" Hiru opened the notes he had written during his amnesia. "My body shrinking was likely an unconscious adjustment of a demon's body to match the state of the mind. But since it's a demon's body, changes in size don't reduce its inherent strength.
What's more vicious than the amnesia itself is the hidden demon blood. If a human were hit by it, they would probably return to the Wisteria House without anything seeming wrong, then slip into amnesia and be discovered, and finally be sent to the medicine house for treatment.
Once everyone believed the swordsman had merely shrunk and lost his memory, the demon blood lying dormant would begin to act. It would gradually remove the body's limitations while eroding the human from within, turning them into a demon.
"Given the combat strength of the medicine house and the permanent staff at the Wisteria House… I imagine a demonized swordsman would get a very satisfying meal."
"Did you discover anything else?"
"Not for now. I still need time to organize the notes from my amnesia." Hiru waved the notebook in his hand. "Luckily, I've always had the habit of keeping records. Otherwise, losing a research opportunity like this for nothing would've driven me crazy.
"Honestly… it's rare to encounter a curse-type Blood Demon Art. If I could experience it again, that would be ideal. I wonder if I can extract more concrete information from the crystal…"
"So this demon didn't die purely because of the Bright Red Nichirin Sword?" Yoriichi asked, looking at the crystal on the table. "Did he stake everything on that final move?"
Hiru nodded slightly.
"After all, he was a demon with a Blood Demon Art. His physical durability was still there. Even after using his Blood Demon Art multiple times and being struck by the Bright Red Nichirin Sword, he should've at least been able to leave some final words."
"But instead, he died the moment his Blood Demon Art erased my memories."
"That can only mean his final Blood Demon Art consumed all of his remaining power, leaving him as fragile as a demon without a Blood Demon Art."
As he spoke, Hiru couldn't help but grab some paper and start scribbling diagrams.
"You know, brother, no matter how you subdivide them, Blood Demon Arts can't escape four major categories.
The first category is the most common: Blood Demon Arts that assist or strengthen the body.
Demons of this type rely primarily on their own physical abilities in combat.
For example, Akaza, whom I encountered before—his Blood Demon Art enhanced his perception, making him extraordinarily sensitive. Enhancements like creating clones, strengthening specific body parts, or even manifesting intangible emotions or personality traits all fall into this category.
The second category is energy-projection-type Blood Demon Arts.That is, releasing the energy within one's body and transforming it into other forms for combat. These are rarer. Manipulating trees or rocks, or creating objects out of nothing using a Blood Demon Art, all belong to this type.
The Blood Demon Art I unconsciously used at first, Banshoku Seki, forcibly suppresses the opponent and extracts their energy. In fact, I could gain more power by devouring those crystals—but thinking about how those demons had eaten humans, and then me consuming demons that ate humans, was frankly nauseating.
So I never did. I just used the crystals as pigments. Though I will say, the finished pigments had excellent color and texture.
The third category is the most troublesome: mental-type Blood Demon Arts. Curses and control both belong to this category. My Blood Demon Art, Painting the World, is a prime example. Through it, I can rewrite others' perceptions, strip emotions from myself or others, and use it without making a sound. It's arguably the most suitable Blood Demon Art for covert attacks.
The final category is the rarest and nearly unsolvable: curse-type Blood Demon Arts. This type has a defining trait—no matter the cost, it can only be activated once.
If we exclude Muzan Kibutsuji's Blood Demon Art used on the Ubuyashiki family, this was my first time encountering a curse-type Blood Demon Art. It's an extremely rare classification.
It's a shame my mind wasn't clear when I was hit. Otherwise, it would've been a perfect opportunity to study curse-type Blood Demon Arts, which would give us more certainty when dealing with Muzan… after all, advanced Blood Demon Arts aren't limited to just one."
"Then… what category does our elder brother's Blood Demon Art fall into?" Yoriichi asked.
"I don't know," Hiru replied, pushing the notebook covered in messy notes forward. "Like you, elder brother doesn't rely on Blood Demon Arts. I did see him use flesh blades during our previous fight, but I can do that as well, so I can't say for sure whether that counts as a Blood Demon Art.
But you don't need to worry too much about that, brother."
"Hm?"
"Because if you get serious, no one can beat you. That reputation of yours as the strongest isn't just empty praise."