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.
Karin-chan starts acting out. Honoka and Shin get some help from Mao-chan to find out why.
Everyone believes Rai-chan to be a very obedient and good boy. When Shiori worries about him not being childlike enough, the Principal shows her another side of Rai-chan.
It's time for arts and crafts at the nursery. Mao-chan is excited to create something for Honoka and works very hard on the present. But when he sneezes and accidentally burns his artwork, he becomes very sad.
Mao-chan becomes fascinated by the remote control and other button-pushing electronics.
Mao-chan and the other devil children meet someone new, but they find it hard to interact with the strange creature.
Mao-chan, Rai-chan, and Karin-chan work to build a house for their new pet. Mao-chan continues to have difficulties as the strange creature attempts to become friends with him.
Mao-chan is a picky eater. The daycare Principal promises Honoka that he will get Mao-chan used to eating cucumbers.
Mao-chan, Karin-chan, and Rai-chan go to the supermarket for the first time on their own. Pepe accompanies them with a camera on his head so that Honoka, Shiori, and Natsuki can watch the children's behavior from the daycare.
The daycare's Principal shows everyone the "Magic Testing Room" where there are many costumes for the devil children to wear and to try different kinds of magic. Mao-chan and the others can use magic from wearing these special costumes even though their Mamas didn't make those costumes.
The daycare's Principal announces to the devil children that there will be a "Lend A Hand" contest. It's a competition to see who can be the most helpful to their Mamas and Papas.
Karin-chan's devil baby wings begin to grow. Itsuki, her Papa figure, uses this chance to play a trick on her.
Rai-chan loves his remote-controlled toy car so much that when Shiori takes it away to get ready for bed time, he rebels the next day at the daycare.
The daycare's Principal and Teacher Ito hold a devil's festival for the children.
The daycare Principal orders a dream picture book that allows all the sleeping devil children to share the same dream when the book is placed underneath their pillows. The Principal chooses to give them the "Big Adventure" dream.
The group continues the Big Adventure by entering the treasure cave.
Mao-chan learns what a kiss is for and begins to give everyone a peck on the cheek to show his affection for them.
Karin-chan goes through a phase of being grumpy and cranky.
The devil children get to see a picture show when they are visited by a storyteller at the daycare.
Kids from another daycare visit Mao-chan's daycare.
Mao-chan wants to Honoka-chan to know that he is reliable by putting on a show of courage. He refuses to cry to show that he is strong and tough. But then, Mao-chan reverts to the form he was when he first appeared before Honoka and Shin.
Mao's childishness has overwhelmed him and he's reverted to a baby! It's up to Rai and Karin to look after him at the nursery.
After Itsuki helps cut Karin's hair, Natsuki will do anything to change it back. So the Principle summons a hairdresser from the Devil World to see if he can help.
Chiyo and Ryuu visit the nursery again.
Honoka buys Mao an umbrella in preparation for the upcoming rainy season. However, it's too early still and it won't rain! So Mao enlists Karin's magic...
The Principle, Ms Itou, Rai, Karin, Mao and Pepe go on a school trip to Pepe's house in the Devil World!
Everybody is enjoying their stay at Pepe's house in the Devil World until they discover the toilet has a secret...
The toilet in Pepe's house is haunted! This is the perfect chance for Mao to try and get over his fear of ghosts and make a friend in the process.
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