Ibu Kirisaki is a Japanese student with long black hair extending past her hips and distinctive red eyes. She battles persistent low self-esteem, frequently seeking solitude by the lakeshore near her school to observe fish.

She attends Kyoukasen Girls' School, an institution catering to students with emotional wounds or lacking confidence. During her time there, a secret romantic relationship blossomed between Ibu and Shun, the school's only male teacher. Their bond began at her frequented lakeside spot. Through this clandestine relationship, she gradually developed self-assurance, though she initially leaned heavily on Shun for direction.

Unbeknownst to Ibu, her sole friend at the school, Himari, secretly harbored romantic feelings for Shun. Ibu envied Himari's popularity and the attention others gave her, contrasting it sharply with her own sense of being an outsider. Ibu also perceived herself as clumsy.

Himari's discovery of Shun's sexual relationship with another schoolmate deeply affected her. This revelation ignited a confrontation between Ibu and Himari over their shared feelings for Shun. Himari attempted to blackmail Shun into a relationship by threatening to expose his existing involvement with Ibu, but he resisted her coercion. Ultimately, Ibu and Himari settled their rivalry by choosing to share Shun rather than continue competing for him.