A second-year student at a university in Yokohama, majoring in Statistical Science. An eccentric who still doesn't own a smartphone. During high school, he encountered various girls suffering from "Adolescence Syndrome." He met Mai Sakurajima, his high school senior and a national actress, through the syndrome, and they are now a couple. He is searching for "Touko Kirishima," who poses a potential threat to Mai.

A nationally popular actress who has made a complete comeback. Previously, she suffered from Adolescence Syndrome where she became invisible to those around her because she couldn't fit into school life due to her busy career. With Sakuta's help, she resolved the issue and returned to acting. She currently attends the same university as Sakuta. Rumors are swirling that she is the true identity of the mysterious online singer "Touko Kirishima."

A second-year student in the Faculty of International Business at the same university as Sakuta. She met Sakuta at a seminar mixer and takes the same lectures; she calls herself a "friend candidate." Like Sakuta, she is an eccentric who doesn't own a smartphone and has a fearless personality. She was the only person besides Sakuta who could perceive Nene Iwami when she became invisible to others...

A high school freshman starting this spring. She suffered from a severe heart disease since childhood, which triggered Adolescence Syndrome. Later, thanks to a donor found through a movie Mai starred in, she overcame her illness and her syndrome was resolved. She had been living in Okinawa for a while to ease the burden on her body, but...

A second-year nursing student at the same university as Sakuta. A serious, honor-student type with a strong sense of justice. She was Sakuta's middle school classmate and felt guilty for not being able to help him when he was isolated for claiming Adolescence Syndrome existed. Her reunion with Sakuta triggered her own syndrome, causing her to swap places with the Ikumi from another possible world. Since resolving it, she has been proactively helping Sakuta search for Touko Kirishima.

Sakuta's friend and high school classmate. She currently attends a science faculty at a national university and works as a part-time tutor at the same prep school as Sakuta. Calm, composed, and highly knowledgeable, she is often consulted by Sakuta regarding Adolescence Syndrome. In the past, she experienced a syndrome where two versions of herself existed due to self-harming behavior on social media driven by loneliness.

Sakuta's younger sister. In middle school, she suffered from Adolescence Syndrome where physical wounds appeared due to online bullying. The mental stress caused her to lose her memory, and for two years, she lived as a different personality named "Kaede" (written in hiragana) without leaving the house. After her memories returned, she challenged high school entrance exams and now attends a correspondence high school of her own choice. She has also started working part-time at the same family restaurant as Sakuta, regaining her cheerful daily life.

Mai's half-sister and a member of the idol group "Sweet Bullet." Due to a complex regarding Mai, whom she had been compared to since childhood, she once suffered from Adolescence Syndrome that caused her to swap appearances with Mai. Despite her flashy look, she is academically excellent; she balanced idol activities and studies in high school and now attends the Faculty of International Liberal Arts at the same university as Sakuta and Mai.

The leader of the idol group "Sweet Bullet," affectionately known as "Zukki" by her fans. She is easygoing and a bit airheaded, often surprising those around her with unpredictable behavior. When she developed Adolescence Syndrome related to her desire to read the room, she struggled with how others perceived her, but she overcame it. She has since dropped out of university to focus on her idol career.

Sakuta's high school junior who starts university this spring. She is a bit clumsy but very sensitive to trends. After being confessed to by a senior her friend liked, she triggered Adolescence Syndrome that caused the same day to repeat, and she came to trust Sakuta during the resolution process. She is also Sakuta's coworker at the family restaurant and has recently become close with Kaede.