Reborn as an Yandere : Yandere X Yandere - Chapter 5: Childhood Crush

After dying in an oddly anticlimactic vending machine accident, Kazuki Ren is reincarnated in the demon realm—not as a hero, not as a villain, but as the only human male student enrolled at the mysterious Academy of Ruin, a school where all the professors are demon lords and all the students are powerful, beautiful she-demons.Ren is told he has one task: survive.But there’s a catch. The Academy’s darkest secret is about to awaken, and Ren holds a hidden power that could either destroy the demon world... or rule it.Now surrounded by seductive demons with hidden motives, eldritch tomes, forbidden dungeons, and twisted exams, Ren must master his ability—or be consumed.Magic, mystery, danger, and temptation await in this dark academia harem fantasy.

A mysterious and strange world, a human civilization lacking power, and a horrible and turbulent world of human life, Luo Kai survived humblely as a prisoner. Pain and suffering honed his will. War and killing promoted his growth. He suddenly looked back. Is already one of the most powerful beings in this world.

- Description from novelbuddy

I possessed a minor character who marries the prince. I’m not thrilled about it. The prince is a scumbag who flirts with the heroine despite being engaged and eventually gets defeated by the original male lead. In the epilogue, all he does is apologize to his fiancée and marry her, with barely a line to his name. Well, his personality is twisted, but at least he’s handsome. And since he’s the third prince, he doesn’t have to shoulder the burden of ruling the kingdom. That’s decent husband material, I suppose. Go ahead, make a fool of yourself. You’re going to marry me anyway. I’ll just sit back and enjoy watching your embarrassing history unfold. “Doris Redfield. Don’t expect me to ask you to dance at this ball. Maybe not at the next one either. Or the one after that.” “Yes, Your Highness. As you wish.” “Even though we’re engaged… wait, what?” “It’s just a joke proposal our parents once tossed around, isn’t it? You don’t need to take it seriously, Your Highness. I’m really fine with it.” “…Is that so? Yes, that’s… fine, right?” Why are you panicking, prince? You started spouting nonsense first. Where’s your conscience? But then, this guy really has the audacity to ask something outrageous. “…Do you, perhaps, have another man?” The guy who flirted with the original heroine is saying this now? Calm down. He’ll regret this later. All I need to do is remain a devoted fiancée until then. “What are you talking about? A woman like me… plain, not beautiful, with a gloomy personality, what man would even—” “What? Who dared to say that about you?” …You did, in the original story. This guy is acting weird. But he’s not the only problem. “My dear little sister Doris, that dress you’re wearing today is dreadful. No wonder there are rumors His Highness has abandoned you.” “Well, it can’t be helped. His Highness is too good for me anyway.” “…Hold on. Too good? Who said that? Wait, were you really dumped?” The original villainess, who also happens to be my older sister, Natalie, is suddenly interested in my love life. Why are all the original tr*shy characters growling at each other over me now?!

This is the story of the youth Wen Leyang, born into the family with an expertise in the cultivation of the Art of Poison.