Demon King Ahriman has a problem: his daughter, Dou, loves everyone! Consequently, Ahriman had to halt his invasion of the world in the worry that his daughter's behavior isn't one befitting someone of her kind. She loves making friends, helping others, and bringing happiness to all creatures including their enemies, the humans.

Ahriman, however, congratulates Dou for her good deeds instead of scolding her. With the help of his aide Jahy, assigned as Dou's master, the two try to get rid of her kindhearted nature—so that the Demon King's daughter goes from a cute, adorable, and nice little girl to an inhuman, cruel, and twisted little demon.