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I think it's about the guy Kamo Noritoshi which is a sorcerer who is inside Getou Suguru right now. He's a really old man from decades or even a few centuries ago. He is able to live through centuries by jumping bodies by transferring his brain into the bodies like Getou's body right now. It seems like he also jumped to Choso's & Yuuji's father's bodies somewhere in past and while living as their father's identities he had choso & yuuji separately. So technically they have different fathers physically but the brain was of the same person that is Kamo Noritoshi. It's like both of their fathers had the same forehead scar like Getou Suguru's.
YOOOO SO HIS DAD WAS THAT EVIL GUY???? SO WHO TF IS YUJI???? I saw someone early hypothesize that Yuji came from the same bloodline as Sukuna and that's why he can be his vessel so maybe that evil dude has something to do with it :O