Responses
I think it's either fragments of the dead guy's soul or ghost/monster parts so that minchan's body gets further away from being human and his own, and slowly morphing into a vessel strong enough to host the other guy's soul. He said it himself to the other guy when they have their battle-off that he changed the entire makeup of his physical body and then chipped away at his mental state
I lowk had a feeling that the great-aunt was a twin cs ik for sure for sure that she that she died but when the “grandma” popped up I was so confused like “how did she come back alive? She must have struck a deal with a god or something right?” But throughout the story with the way Minchan talks about his great aunt, it doesn’t sound like something she would do necessarily, his great aunt didn’t seem like a bad person, then all of sudden it was a lie and she actually survived and was doing evil deeds????? Then plot twist it was actually the grandma doing the bad deeds while the great aunt died. Minchan was young and his grandmother was never there so I understand why he probably mixed the two together BUT what is that red stone that “Mr. Whatever” (idk what to call him) gave Minchan like is that what made him forget about his childhood so he can take his soul and shit and bring back that dude that looks like him? Or is the stone actually good and actually helping get stronger and he is just doing good deeds so in the future Minchan doesn’t suspect him as a bad guy? Personally I think it’s the second one