I Beat the World-Destroying Villain into a Love Brain

[The heroine with the ceiling of force value + the male protagonist who is reborn in dankness + falling in love and killing each other + self-strategy + love brain] The system asked me to save the villain, so I went. No one believes in the rebirth of villains, so guarding against me is like guarding against thieves. I was too lazy to coax and just started fighting. After beating him, he became immortal, and every day he thought about how to get me to look at him one more time. I'm just wondering, how come you, a world-destroying villain, have a brain for love?