Once most students are done with high school, they leave and never come back. However, at 25 years old, Hana Natori finds herself in the role of a student once more at her aunt's request. Since Hana's cousin, Kaho Miyoshi, refuses to go to school, her aunt begs Hana to take Kaho's place, since the two of them are practically identical. But as luck would have it, she is recognized by Okito Kanie—an old classmate from her days in high school—who is now a teacher! With her cover blown, Hana assumes Kanie will expose her secret. But when he suddenly kisses her, she soon learns he has other ideas.

Two years after meeting Aoi, Kaoru and gang are still up to their normal habits. Kaoru now in grad school and the tenants being as rowdy as ever what will become of Aoi and Kaoru's love. Two years has passed since Aoi and Kaoru were freed from the bonds of their families. They continue to live their normal lives with their usual friends in their house.

Kaoru Hanabishi, a college student who lives alone, met a beautiful but bewildered girl dressed in a kimono at a train station. He volunteered to guide her way to the address she was looking for, which happened to be in his neighborhood, but turned out to be an empty lot. Not knowing what to do next, Kaoru invited the devastated girl to his apartment and asked for any additional clues to her destination. She supplied him with a photo of two children whom Kaoru immediately identified as himself and Aoi Sakuraba, his childhood friend. It turned out that the girl in front of him is Aoi Sakuraba herself, his betrothed fiancee who came all the way to Tokyo to marry him. Her revelation was not only surprising but also reminded the deepest part of Kaoru's memory for why he left the Hanabishi family in the first place.

Chiyo Mihama begins her high school career as one of the strangest students in her freshman class—a tiny, 10-year-old academic prodigy with a fondness for plush dolls and homemade cooking. But her homeroom teacher, Yukari Tanizaki, is the kind of person who would hijack a student's bike to avoid being late, so strange is a relative word. There certainly isn't a shortage of peculiar girls in Yukari-sensei's homeroom class. Accompanying Chiyo are students like Tomo Takino, an energetic tomboy with more enthusiasm than brains; Koyomi Mizuhara, Tomo's best friend whose temper has a fuse shorter than Chiyo; and Sakaki, a tall, athletic beauty whose intimidating looks hide a gentle personality and a painful obsession with cats. In addition, transfer student Ayumu Kasuga, a girl with her head stuck in the clouds, fits right in with the rest of the girls—and she has a few interesting theories about Chiyo's pigtails! Together, this lovable group of girls experience the ups and downs of school life, their many adventures filled with constant laughter, surreal absurdity, and occasionally even touching commentary on the bittersweet, temporal nature of high school.