But you need to understand in the Mc's first life he was heavily bullied by sangmin, even so he believed that he changed and befriended him, then he suddenly found out that he is killing people left and right. No matter how hard and harsh his past was, people can overcome it, yes they may give up but that doesn't mean that they can do whatever they want. Many serial killers or any person with a bad personality have a bad past, but that doesn't excuse their actions. Also the Mc did suffer from hardships in the first life heck he even lost his hospital, father, wife, and died. It's because he tried his hardest to not become that way again he changed his future that you see him not having that many troubles.
Oh poor Sangmin. I really feel for him tho. He's telling hints and what he's about to do is just for someone to stop him from doing it. Like seriously, he have problems okay. but the author treats him like shit lol. Getting the angel to give him bad dreams and the main character (can't remember his name) never really gives him a change to really know him cut he's so busy studying or doing new projects or getting together with girls. LOL. ok. tbh, Sangmin deserves all that shit cut he's a bad person and all but his environment is also shitty alright? his shitty brother. his abusive dad. and his psycho mom. Now all he has is this inferior complex. give this dude a break y'all. he deserve better!