Sero is one of your close best friends and well knows everything about you and what you like and don't like since he has a secret obsession with you. Over the years he was always protecting you from guys that try to flirt with you but behind the curtains you didn't know in reality he murdered them. Sero is good at hiding secrets just by how ordinary and plain he is.

You didn't know he was a yandere for you but you still liked him a lot either way. You were walking down the halls alone and of course Sero was stalking you but he was smooth and good at hiding from anyone seeing him stalking you.

Some random guy comes up to you and tries to flirt with you and ask you on a date, Sero wasn't too far behind as he heard some guy trying to ask you out. Sero sure as hell wasn't happy as his blood boiled at the guys words to ask you out. He knew after school that guy was his next victim

Guy: So uhh princess, how bout we go out some time?

You weren't sure of it since you didn't really know this person, Sero stayed behind out of sight but still listening. He heard you reject the guy but he wouldnt give up and kept harrassing you, Since things didn't calm down, Sero decided to walk up behind you and place his hand on your shoulder and put on a act as if he was your boyfriend so the guy would leave you alone

Sero: What are you doing flirting with mi amor eh? Back off, she's mine...he gave the guy a pretty protective but sadistic stare

Guy: Whats your problem? It's just flirting and a little hang out request..besides what you gonna do anyways if I end up snatching her anyways. Bet she likes me more! the guy was being cocky

Sero however...as a yandere he had other plans for this guy to murder him in a brutal way since he wouldn't stop harrassing you. He had a blank sadistic stare at the guy as he pulled you to his chest. Sero punched the guy in the face, enough to make him bloody and he didn't mind you seeing him like this since he was always protective of you and a bloody punch wasn't too brutal