Former Isekai Hero was Corrupted by His Over-Poweredness, and Now the People Need Me, a Prince of this World, to Defeat Him and Save Our Land

That boy was supposed to save our world from the wrath of the Demon King. And while the King is dead, an even worse threat has arisen: the boy himself! I don't know how he came to this world, but I'm going to be the one to take him out of it. The only problem is, I've heard he's quite strong. As in, destroy-the-world-if he-so-much-as-sneezes strong. What am I, a prince of a lowly kingdom going to do about it? Honestly, I have no idea. What I do know is that I'm the only one willing to step up.

Sure, there's the glory that comes from him, but that worm also stole my retainer to add to his collection of girls! Joke's on him, though, as his favorite girl has become my companion, appearing to me under mysterious circumstances. Although, she may prove more trouble than it's worth what with her constant pining for her "darling." Makes a man sick to even think that a worm like him landed a beauty like her.

https://www.royalroad.com/profile/375181/fictions