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.

Honoka meets some of the other parents and learns that demon children possesses abilities depending on what costume is worn. They use these abilities to protect their parents.

Honoka becomes intimidated by Shin when he constantly scolds her for her clumsiness. Later that night, Mao-chan comes down with a fever.

Reading the book that the Principal gave her, Honoka stops Mao-chan's fever by allowing him to release magic. As Honoka and Shin reconcile, Honoka's aunt, Rikako, comes home and is surprised when she sees Mao-chan.

With Shin's help, Honoka expresses her lonely feelings to her Aunt.

Honoka attends a practice for a play date with the mothers of the other devil children, Natsuki and Shiori, who don't get along with each other.

Following Shin's advice, Honoka tries to help everyone get along by encouraging the children to play together.

It is the day of the play date and everyone manages to get along.

Mao-chan spends his first night without Honoka at the nursery, but it doesn't seem to be going so well.

Mao-chan and friends take a test of courage while spending the night at the nursery. They have to get pass all sorts of obstacles. The frightened devil babies try to overcome their fears together.

Honoka's time with Mao-chan has come to an end. Soon after leaving, she realizes that she loves Mao-chan and runs straight back to the daycare center.

Honoka and Shin get to meet Karin-chan's father figure, who turns out to be Natsuki's younger brother, Itsuki. Itsuki goes to the same school and in the grade as Honoka.

Honoka begins to realize her feelings for Shin.

Mao-chan gets jealous when Honoka is not paying attention to him and tries to get her attention by throwing a tantrum.

Natsuki helps Honoka and Shin look for Mao-chan. Itsuki finds Mao-chan in an unexpected place.

Honoka and Shin take care of Rai-chan while Honoka tries to convince Shiori to come back as Rai-chan's Mama.

Honoka continues to be persistent until Shiori's true feelings are revealed.

Honoka reflects on some of her encounters with Shin.

Mao-chan is introduced to other kids at the park.

Mao-chan is the last to stand up and walk.

It is Sports Day at the Chibi Devi Day Care. Mao-chan competes against Karin-chan and Rai-chan.

Honoka catches a cold and needs to rest for the day. Shin does his best to take care of her and Mao-chan.

Honoka is encouraged to confess her feelings to Shin.

When Mao-chan and the other devil children have to get inoculated, Shin needs to get over his fear of shots to help them. In the end, Mao-chan spoke his first word.

After having spoken his first word, Mao-chan learns to say new words. Karin-chan and Rai-chan have also begun to talk. One month later, Mao-chan reveals a secret!

It is awkward between Honoka and Shin since Honoka automatically avoids Shin. Mao-chan is initially very confused but then becomes determined to get his parents to reconcile, believing them to be fighting with each other.