Puberty syndrome – Abnormal experiences rumored on the internet to be caused by sensitivity and instability during adolescence. This year, Sakuta Azusagawa, a second-year student at a high school near Enoshima, meets several girls that are experiencing this “puberty syndrome.” For instance, he meets a wild bunny girl in the library. She turns out to be an actress on hiatus, Mai Sakurajima, who is also his senior at the school. For some reason, no one else can see this enchanting girl. How did she become invisible…? As Sakuta searches for answers to help Mai, they spend more time together, and he eventually learns of her hidden feelings… This is an unusual story that takes place in a town of bright skies and glistening seas, where Sakuta encounters various intriguing girls.

Sakuta had been unable to see Mai, who was not only busy with work but had an order from her agency forbidding her from going on dates. The second term finally begins, and Sakuta is eagerly looking forward to seeing Mai again at school. But upon seeing Mai in front of his house, she greets him with a shocking, "Who the heck are you?" Upon confirming what the circumstances are, it comes into light that Mai and her little sister Nodoka Toyohama have swapped bodies. Until this new Adolescence Syndrome is resolved, Mai will be living as Nodoka, and Nodoka will be living as Mai...

With Nodoka's Puberty Syndrome resolved, Sakuta's expectations to spend sweeter times with Mai is growing. But then, a scandal is reported by the media about Mai Sakurajima having a new boyfriend. In the press conference for a movie she had a role in, Mai gives a sincere explanation. Seeing that, Kaede decides to set goals for the rest of the year, wanting to do her best for Sakuta's sake as well. One of the goals she writes down is to go back to school...

With Sakuta's help, Kaede is able to go to school at night. She is now enthusiastic about heading to school during the day. However, on the following day, the original Kaede's memory suddenly returns, eradicating all memories of the Kaede that had spent the last two years together with Sakuta. A certain person appears before Sakuta, who is overwhelmed with grief because Kaede was no longer around.