Mercenary adventurer Theo Aspel is tragically weak, leaving him no choice but to repeatedly joins various parties―only to get kicked out. In order to get stronger, he succeeds at summoning a demon that will grant him a wish. But the minute he sees her, his wish to get stronger flies straight out the window. This devil, who hadn’t been summoned in many years declares: "I will grant your wish, but you must give me something precious to you."