Even after leaving Fujisawa for Ogaki, not one person remembered anything about Mai Sakurajima. Sakuta and Mai return to school together, but even there they hear from Sakuta's friend Rio Futaba that nobody at school outside of her has any recollection about Mai. At the same time, Sakuta hears of a theory that losing memories concerning Mai is based on a certain action taken, and struggles so that he doesn't lose his memories of her. And seeing Sakuta act as such, Mai makes a certain decision of her own as well...

It is now the last day of the first term, the promised day when pretending to be dating Tomoe ends. It seems as though everything has finally been resolved, but…

Sakuta unveils to Mai and Nodoka the details of his family's past, and the trauma that Kaede underwent. Meanwhile, Kaede continues her re-integration into society, but as more hurdles appear, Sakuta worries for his sister's well-being.

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.

While looking for the cause of Mai's Adolescence Syndrome, Sakuta ends up scheduling a date with Mai. On the day they promised, Sakuta tries to help out a lost little girl on his way towards Fujisawa Station. But, he is misunderstood to be a perverted maniac by another girl, and because of that, he ends up arriving late to his appointed time to meet Mai. He somehow gains Mai's forgiveness and they proceed with their date, but Mai changes their destination, and takes Sakuta to Shichirigahama Beach...

Upon inducing a case of "Puberty Syndrome" where two copies of herself exists, Rio ends up staying at Sakuta's house for the time being. Meanwhile, "the other Rio" has been busy posting various unexpected photos on social media. After being informed about these activities by his classmate, Saki Kamisato, Sakuta decides to have a chat with "the other Rio." As he learns more about each of the Rio-s in hopes of discovering the reason for "the other Rio’s" actions and possibly a cure for her "Puberty Syndrome," Sakuta begins to realize the troubles each of them carries...

Sakuta has started attending university and meets a girl during a group outing.

Because of the misunderstanding that she was dating Sakuta, Tomoe is able to resolve the agonizing situation of being asked out by the guy her friend is in love with. She pleads with Sakuta to continue acting like they are dating. Despite feeling indebted to Mai, Sakuta could not leave Tomoe alone as she was fearing that she would lose her presence within her class. So, he reluctantly agrees to play the role of Tomoe's fake boyfriend for a while.

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...

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.

Unable to deal with a commercial filming well as the actress Mai Sakurajima, Nodoka gradually starts to feel a strong sense of inferiority. As their body-swapped lives continues on, the day arrives where Mai must perform in Nodoka's pop idol group "Sweet Bullet". Sakuta and Nodoka attend the concert as they were given tickets...

After agreeing to harbor an abandoned cat, Sakuta finds himself welcoming a look-alike to his old school crush into his home. This does not sit very well with Mai, who is trying her best to be with her boyfriend amidst a demanding work schedule. Meanwhile, something appears to be up with Futaba...

Uzuki begins blending into her friend group’s dynamic as her popularity grows.

It’s the day of Sweet Bullet’s performance in an ensemble concert at a venue in Odaiba.

A Miniskirt Santa suddenly appears before Sakuta. She says her name is “Touko Kirishima” and claims to have been handing out Puberty Syndrome to people as gifts. Sakuta sees her eyes lock on Ikumi Akagi, a former middle school classmate who is attending the same university as Sakuta, studying in the nursing program. Curious about Ikumi, Sakuta goes on a group date with female nursing program students that his friend invited him to. There, they discuss a rumor about people’s dreams coming true after they post about them on social media with the hashtag #DREAMING...

A pumpkin lantern made of glass comes crashing down in a plaza in front of Sakuragicho Station, just as a social media post with the hashtag #DREAMING had predicted. However, Ikumi rushes in to protect a girl who was running directly underneath it as it falls, preventing any injuries. She believes the rumor about the #DREAMING posts and has been going around saving people. Ikumi visits Sakuta at the university and passes him an invitation to their middle school reunion. Sakuta warns her about helping people too much, but she ignores this advice...

A poltergeist-like phenomenon attacks Ikumi. Sakuta is worried the attack was caused by Puberty Syndrome, but Ikumi claims that the only way to fix this problem is by forgetting about Sakuta’s existence. Hearing this, Sakuta is stunned and confused. Without giving him the time to compose his thoughts, Ikumi proposes that they have a contest, competing to see if Sakuta will remember “that day” first, or if Ikumi will forget about Sakuta first.

Upon searching the hashtag #DREAMING, numerous posts were found about attending a middle school reunion on November 27th. Ikumi also dreamt about the day of the reunion, but in her dream, she injured someone and was arrested. Sakuta invites Ikumi to visit Minegahara High School, and there, he shares with her the various bizarre things about her that have been bothering him. On the way home, Ikumi suddenly says goodbye to Sakuta as they stand facing each other with the railway tracks in between them…

Sakuta sees a familiar Miniskirt Santa on a beauty pageant website that his friend Takumi Fukuyama was looking at. However, he notices that her name isn’t listed as Touko Kirishima, but rather as Nene Iwamizawa. As he continues his search for Touko Kirishima, he receives an offer of help from Sara, which he accepts. One of the symptoms of her Puberty Syndrome includes knowing what a person she has collided with is thinking, and that’s how she figured out that Sakuta was looking for Touko Kirishima. Sara suggests reading the Miniskirt Santa’s mind at the venue where she’ll perform her new song live on Christmas Eve.

Soon after Mai's "puberty syndrome" is resolved, Sakuta encounters another strange phenomenon without respite. Day after day, it is the same day for Sakuta and there is no tomorrow. When he consults Rio, she raises the possibility of "Laplace’s demon" -- that someone may be repeating and redoing a day.

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...

Sakuta from the other possible realm sends a message through Ikumi that reads, “Find Touko Kirishima, Mai-san is in danger.” After seeing this message, he tries contacting the Miniskirt Santa, who claimed to be Touko Kirishima. A few days later, he receives a call from her saying that she can meet on December 2nd… which also happens to be Mai’s birthday.

Sakuta dreams that on Christmas Eve, when he is meant to have a sleepover date with Mai, he instead goes on a date with a student named Sara Himeji from the cram school where he works. The Sara in question has the same dream as Sakuta and goes on to confess that she has her own Puberty Syndrome. However, she says that she does not want her Puberty Syndrome to be fixed. Sara developed Puberty Syndrome after a heartbreak, and the symptoms of her syndrome ease her anxiety by making her popular with guys, which she has been enjoying. Sakuta warns her that this is a dangerous move. To which she retorts to provoke him, “What should I do so that I can love people. Like you do, Mr. Sakuta?”

Sakuta has a dream that Mai reveals herself as the true identity of Touko Kirishima at a music festival held on April 1st. At the same time, several major social media platforms were being flooded with posts containing the hashtag #DREAMING, leading to platform crashes and access errors. As the hashtag #DREAMING causes chaos among the public, Tomoe Koga tells Sakuta that she had a dream that Mai got into an accident, rendering her unconscious during an event where she was collaborating with the police for a public safety awareness.