Rui Ijigawa is Honmaru Edojo's classmate and Iyona Kawai's best friend, recognizable by her large ribbon. She reveals a cunning, mean-spirited nature, frequently targeting Honmaru with pranks and harassment. This behavior originates from unresolved childhood feelings; Rui secretly harbors attraction for Honmaru but responds with anger and hostility stemming from his past rejection. Despite her overt bullying, hidden care surfaces, such as keeping personal photos of Honmaru during vulnerable moments like crying at vaccinations or struggling with his water phobia during swimming.

Her interactions show layers; when Honmaru assists her, Rui displays moments of genuine gratitude and femininity, blushing or reacting tearfully. She plays as a setter on the volleyball club alongside Iyona, maintaining their friendship despite contrasting personalities. Rui proves notably strong-willed and unafraid of confrontation, even resisting intimidation from figures like Mimora. She once manipulated Mimora's magic to escalate her harassment of Honmaru, threatening to "kick him out of the house."

Throughout the series, she gradually acknowledges Honmaru's development, particularly as he masters various sports. Their dynamic involves belligerent tension hinting at mutual, conflicted attraction, played out through pranks and retaliations. Rui, Honmaru, and the bully Jabao Jaba share a long history as childhood friends, having attended kindergarten, elementary school, and junior high together.