The Pleasure of Defeat

I'm a demon who got reincarnated as a human in Japan; now I'm living a peaceful life as an ordinary salaryman. But lately, a magical girl's been coming after me to try and "vanquish" me. Even with only a fraction of my former power, I defeated her easily, and I decided to take her virginity as my "prize" for winning. Ever since then, she's been challenging me to one rematch after another, and I've been defeating her and fucking her every single time. She knows she's no match for me at all, but for some reason, she just keeps coming back...