Hotaru is remarried and has a child. While she is satisfied as a wife in her relationship with her husband, she lacks fulfillment as a woman. One day, while she is pleasuring herself alone, she is discovered by Koichi, her stepson. This encounter complicates their familial bond. Meanwhile, her biological son, Takao, returns home for a visit. Caught between the affections of both sons, the mother can no longer suppress her deepest desires, ultimately giving in to forbidden passion.