Rumi is a girl who transferred into Kōhei's school. She used to be in the kendo club but had to quit after hip complications. Her goal is to become a "true maiden" and to that end, she behaves maidenly toward those around her, but she shows her true character just to Kōhei who left a terrible first impression. She does not belong to any club, but she tries to join in literature activities. She likes her old school's uniform, and even though she has the new school's uniform in her possession, she continues to wear her old one. She is bad at putting her own hair into pigtails and while she never says them herself, the phrases Kōhei imagines her saying are well-known by fans of the game.

From Wikipedia.