Honoka Sawada is a sad young girl who lost her parents and is constantly picked on by her classmates. One morning, she wakes up to find a strange baby with a devil's tail named Mao. As Honoka is once again picked on by her classmates as she goes to buy some milk, Mao-chan responds by blasting them with some fire.

Honoka calls her childhood friend, Kyou Toono, and his classmate, Shin Sugisaki, to see Mao-chan. When Kyou leaves to watch his favorite anime, Mao-chan escapes the apartment.

As Honoka and Shin search for Mao-chan, Mao-chan's exploration leads him to the top of a roof. Mao-chan is saved by a strange person who knows Mao-chan's true nature.

The man reveals himself to be the director of a daycare for devil children such as Mao-chan. When Honoka feels uneasy about becoming Mao-chan's surrogate mother, she agrees to take care of him for a month while the director finds a replacement.

Mao-chan becomes grouchy towards Honoka after being left at the daycare center for the first time, but Shin manages to set things straight. Afterwards, the director gives Honoka an invite to a welcoming party where she'll meet the parents of other demon children.