Ore to Omae no Stalker Boushihou
Aishite Kudasai, Sensei
I have a fascination with yandere, especially male yandere, and this boy takes the goddamn cake and eats it because he's basically the epitome of a male yandere if I've ever seen one. He even asks if what he was feeling "[wasn't] love, then what is it?!" and the only answer I could think of was "obsession," and that's EXACTLY what a yandere should be imo. Even going to the lengths of trying to have sex with another girl while the object of his affection is in the same room so he could "make love to her" that way, brilliant.
Dear, Crazy Monster
I should have observed this a little closer because funnily enough, I thought this one was just a fluff piece. Good LORD was I wrong. Our main character Hayato is a little ball of CRAZY. He's the titular Crazy Monster, and man does he live up to his name. Not wanting his big brother to continue being cold to him, he follows him one night to find out he's been prostituting himself. Hayato gets annoyed and from there he starts spiraling down into stalking, blackmailing, and even imprisoning his brother.
Itou-san (KURAKA Sui)