Tomoe Koga

Birthday - May 23, Height - 152cm

The heroine of Volume 2. She first appears in Volume 1. She has slightly quirky short hair, with the left side of her bangs held together with a hairpin shaped like the letter "T".

She is a junior to Sakuta by one year and belongs to Class 1-4 at Minegahara High School. She is one of Sakuta's few friends. Originally from Fukuoka Prefecture, she moved after graduating from middle school due to her father's job transfer. At the same time, she changed her hairstyle and other aspects to blend in with her new surroundings and tries to hide her Fukuoka origins by always speaking in standard Japanese, although her native Hakata dialect slips out when she is flustered or excited. Sakuta sometimes mimics her dialect.

She has a strong sense of justice but is also somewhat clumsy. During their first meeting, she mistook Sakuta for a suspicious person and kicked him. After realizing the misunderstanding, she asked Sakuta to kick her back as an apology (Sakuta described it as "a relationship forged by kicking each other's butts"). Later, she started working part-time at the same family restaurant as Sakuta and Yuma, where she is often teased by Sakuta for being sexually harassing. She is conscious about her large buttocks and often talks about dieting because she worries about looking fat.

In Volume 2, she and Sakuta repeatedly experience the same day due to a puberty syndrome, leading Rio to call her "Laplace's Little Devil" (as Rio theorized she was simulating the future, not reversing time), and Sakuta referred to her as "Petit Devil." After the incident, she continues to interact with Sakuta as a junior and friend.

Having moved from Fukuoka, she has few friends from high school and is extremely afraid of being alone (or being perceived by others as such). She desperately tries to keep up with everyone's conversations and reads the room like a typical modern high school girl.

By Volume 10, she is a third-year student, has grown her hair to shoulder length, and has become close friends with her junior at the family restaurant, Hanakaede, earning Sakuta's gratitude. She secured a recommendation for university and submitted her application, and by Volume 11, her acceptance was confirmed.