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 super 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 hero part, but that worm also stole my attendant to add to his collection of girls! Joke's on him, I've got one of his girls as my companion, though this one seems to be dumber than a sack of rocks.
Just my luck.
Together, we'll travel to the Demon King's palace to somehow put a stop to this threat, or my name isn't Anno, third prince of Cross!