After I Beat the Game, the Demon Lord Became My Familiar

Why does a hero have to kill the Demon King? Especially when the Demon King is a cute girl?

Wouldn't it be wonderful to use a hidden item to turn her into my familiar and have her do the laundry and cook?

I don't know who wrote the program with their feet, but somehow I actually succeeded. Unfortunately, there was a bug, too. System error: I didn't return to my original world.

And so, with the Demon King turned into his familiar, the hero Aijien began a New Game Plus adventure on HARD mode, without any guidance from the System.

This novel and its characters are entirely fictional. Any resemblance is purely coincidental. Do not imitate.