Growing up can be painful. Especially when you fall down a flight of stairs, suffer severe head trauma, and wake up with the mental capacity of a kindergartner. Ouch! Now, 17-year-old Nanaka Kirisato has to grow up all over again. If she thought fitting in as an unpopular bookworm was hard, subtracting eleven years certainly won’t help. Throw in a mullet-headed boy bully, a karate-chopping girl bully, a bullheaded best friend, and a barrage of schoolyard battles, and Nanaka's problems multiply infinitely!
Seventeen-year-old Nanaka Kirisato is a high school student, who’s serious about her studies and goals in life. She frequently criticizes her childhood friend, Nenji Nagihara, for being a childish delinquent who spends his time fighting other boys. After a heated argument with Nenji, she falls off a flight of stairs and suffers a brain injury, resulting in her mind reverting to that of a six-year-old!
Nanaka used to be very cold and unsociable but now she’s completely opposite. People in her class have begun to be suspicious about her. Nenji, who knows what exactly happened to her tries his hardest to keep the secret from others.
Jinpachi’s sister believes her brother should be more disciplined as the person who ought to carry the future of the Arashiyama Family and the family dojo. Satsuki witnesses her brother acting weird around Nanaka and thinks that she is the person who is bringing him down and decides to dispose of her.
Amemiya always knows how nice Nenji can be to others because he helped her when she was being bullied eleven years ago. Anemiya catches a cold and goes to a hospital, but discovers Nanaka’s secret.
Nenji saves a kindergarten student being bullied by a high school delinquent. Now the girl, Kuriko, is in love with Nenji.
Nenji, Nanaka and the others visit Kyoto for the school trip. During free time, they walk around in town and agree if anyone gets lost to meet in front of the big cherry blossom tree. Nanaki ends up lost and walks around searching for the others, but a random student bumps into her on the stairs and she reverts back to seventeen.
Nenji explains to Amemiya that Nanaka is back to normal. Despite cold looks from the others, Nanaka is all over Nenji, and they spend their free time together.
Nenji has a cold, and Nanaka visits him at his home to take care of him. Amemiya and Kuriko also show up to look after sick Nenji. They’re all supposedly taking care of Nenji but he only gets sicker.
Nenji tells Amemiya he wants to take her out for a movie as a way to say “thank you” for helping him study. But when they get to the movie theater, she sees Nanaka. Amemiya comes up with an excuse so they can leave the theater. But the people she knows show up everywhere she goes.
The school Cultural Festival is only one month away; Nanaka suggests the theme should be Magical Domiko, and the entire class agrees. Kazamatsuri suggests Nanaka to take the role of director and screen play too. Later, Nanaki passes out.
Nanaka reverts back to six years old; the next day at school, the class demands that she announce the cast members for the play. Seventeen Nanaka has finished writing the play, but six year old Nanaka has no idea about the play.
Nanaka gets very depressed after she found out that her favorite TV show “Magical Domiko” is going to end. She wakes up dressed up just like Domiko. And the next second she finds herself inside of the world of Magical Domiko. Nanaka is now experiencing various things as Domiko in the story.
Nanaka disappears and her father contacts Nenji and asks him to help him look for her. When Nenji finally finds her, she is back to her seventeen year old self. Nenji is upset and confused but tries to talks to her. During the talk, she tells Nenji she wants the six year old Nanaka to disappear.