From what I think, I think either tsukasa was possessed and somehow was able to come back or his real self was left in the house and someone exactly like him was created in replace of him but evil to me the real tsukasa and the fake have some what of the same personalities they both seem to love hanako and have reckless and kinda socio or psychopathy kind of behavior like at tsukasas age he literally sacrificed himself for hanako which is weird for a kid his age but then since he's replaced with some evil spirit version of him the fake tsukasa just wants to in a way mentally torture or kill people around him . Its just a theory of mine anyways I'm I'm happy we're finally getting on touch with tsukasas backstory he's literally my favorite character!
From what I think, I think either tsukasa was possessed and somehow was able to come back or his real self was left in the house and someone exactly like him was created in replace of him but evil to me the real tsukasa and the fake have some what of the same personalities they both seem to love hanako and have reckless and kinda socio or psychopathy kind of behavior like at tsukasas age he literally sacrificed himself for hanako which is weird for a kid his age but then since he's replaced with some evil spirit version of him the fake tsukasa just wants to in a way mentally torture or kill people around him . Its just a theory of mine anyways I'm I'm happy we're finally getting on touch with tsukasas backstory he's literally my favorite character!