Grimoire x Reverse: Tensei Kijin Romantan

Inside a mid-boss room, waiting for the hero, a demon gets his former-life's memory back and realizes that he's in a RPG game he played.
Knowing that in his previous life he was just an ordinary college student, he is not content with being a to-be-defeated mid-boss. Determined, he decided to defeat the boss and escape the dungeon. In doing so, he is tasked by a goddess to find special "pearls" scattered across the world.