Rio Futaba

Birthday - October 23, Height - 155 cm

The heroine of Volume 3. First appearance is in Volume 1. A second-year student at Minegahara High School and a member of the science club. Usually wears glasses but sometimes wears contacts, especially more often as a university student. Her long hair is slightly wavy and usually left down, but sometimes she ties it into a ponytail.

One of Sakuta's few friends and a confidant. She is the person who named Sakuta "Adolescent Pig" and frequently calls him "Pig" among other things. Despite her sharp tongue, she sees Sakuta as a friend and always listens to his troubles while complaining. She has been aware of Kaede's dissociative disorder and Shoko Makinohara's story since before Sakuta started dating Mai. In Volume 8, she mentions that she finds Sakuta "unexpectedly reliable," stemming from the time he helped her with her Puberty Syndrome.

She rarely shows emotions, speaking in a logical and analytical manner, even about herself, often appearing detached. Combined with her usual lab coat and eccentric rumors, she was isolated from others until she spoke to Sakuta, who was similarly isolated, in their first year and they became friends.

Kunimi Yuma, a mutual friend with Sakuta, was also their classmate in the first year. She has feelings for Yuma but only interacts with him as a friend.

She is uncomfortable with male attention and wears a lab coat over her uniform to hide her large chest, disliking the attention her body receives. She has a self-deprecating view of her appearance, including her facial features.

As the sole member of the science club, she conducts activities to keep the club from being disbanded, almost privatizing the physics lab. She is known as an eccentric for causing incidents like blackouts and minor fires during experiments. She is knowledgeable in physics and often discusses or explains Puberty Syndrome to Sakuta through quantum theory and relativity.

Her father is a university hospital doctor, and her mother runs an import brand apparel shop. Both parents are often absent due to work, leading her to live alone for about six months at a time, making her capable of cooking and doing laundry. Her nearest station is Hon-Kugenuma Station.

In Volume 10, after graduating from Minegahara High School, she attends a national university in the sciences. Although attending different universities, she and Sakuta continue their friendship and work as tutors at the same cram school. She also keeps in touch with Yuma, and in Volume 11, she reunites with him and Sakuta after Yuma completes firefighter training.