Man, I hope Yooyoung's soul is long gone. I'm gonna roll over if I see him fighting back just to hurt MC.
There's a possibility it'll be a plot device later on when ml and mc get together for real. Cuz one thing I thought is that yooyoung's soul might've been not gone, but severely weakened after the accident which let yooyeon either suppress it within the body or exchange places with it meaning yooyoung's soul is now the lingering spirit, and when they get together for real yooyoung will try taking his body back and mc and ml will have to fight against it somehow. I'm not sure if yooyoung has his old memories bc if that's the case he might actually just be a victim as he's not yet the abusive guy he once was, although I suspect for the sake of the main couple he'll be a villain who was trying to get close to mc to hurt him even without his previous life's memories
So I saw someone saying ml is a combination of the two brothers? Which I get but don't quite agree with. I think the body is yooyoung (black hair), and after the accident the soul is yooyeon (white hair) whom I theorized previously to have remained on earth as a lingering spirit and didn't reincarnate, since he retained all of his memories and can see dead spirits (likely because he's not fully integrated into yooyoung's body and is still partially ghost), I believe he was something akin to the creepy guy's dead son who also didn't reincarnate and instead lingered and retained the memories of his father, or at least the hatred he felt, whereas mc who DID reincarnate lost them all till the curse took hold and cannot see spirits. He probably followed mc/yooyoung as a spirit and took yooyoung's corpse after the accident, but ml is not a mixture of their souls, rather yooyeon substituted yooyoung, as ml had major personality changes and lacks several of yooyoung's memories like his friends and ID, he also acknowledges they're not the same person when confronted. I think yooyeon could eventually take over the body completely and retrieve yooyoung's memories, but yooyoung's soul is probably gone gone.