Onee-san wa Joshi Shougakusei ni Kyoumi ga Arimasu.

Minori Yamada is a high school teacher who harbors an unwholesome fascination with young girls. Her life becomes increasingly complicated when her roommate, who frequently brings home a young girl named Coco Suzuhara to care for, inadvertently exposes Minori to the child's innocent charm. As Minori finds herself increasingly drawn to Coco's youth and vulnerability, she must navigate the blurred lines between her pedagogical responsibilities and her disturbing urges. Minori's daily life is further complicated by her relationships with Coco and her roommate, who seems oblivious to the adult's growing infatuation with the minor. As Minori struggles to reconcile her desires with her professional obligations, she must confront the consequences of her actions and the moral implications of her behavior. In this delicate balancing act, Minori must walk a fine line between her professional duties as a teacher and her perverted inclinations, all while trying to maintain a veneer of normalcy in her life. The situation is made more precarious by the presence of Coco, who unwittingly becomes the focal point of Minori's obsession.