Deep within the Black Forest teeming with poisonous mushrooms, a witch named Luna lives alone. With skin that is poisonous to the touch and a breath that will kill if close enough, she is forced to stay secluded from nearby civilization. Even with these conditions, Luna still visits a nearby city to deliver medicine and buy new books to read. Despite Luna having never done harm to any of the city’s residents, many are scared to associate with her, as she is a black witch in a kingdom ruled by white witches. Only able to watch from a distance while people receive her medicine and freely converse with one another, Luna is drawn toward their lives, even if it sometimes means putting herself in danger.

Yakou, a gentle human woman, works at a detective agency. Tounome is a smart and gentle invisible man. The invisible man's ability is perfect for detective work. However, the blind Yakou can still figure out where Tounome is, even if he disappears. Before they know it, the two become attracted to each other...?

Welcome to the fascinating world of Gensokyo, in which youkai (A term for all sorts of spiritual creatures), animals and some humans live, completely separated from our world by a magical barrier. The only gateway between the two worlds is the Hakurei shrine. Reimu Hakurei is the maiden working at said shrine. Whenever problems of supernatural causes (known as "Incidents") occur, Reimu goes out with her friends to investigate, eliminate the cause and hopefully restore Gensokyo to its equilibrium.

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 is not 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, who is 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.