After losing her husband, Eri continues living with her two sons. The elder, Nobuo, is a responsible working adult, while younger brother Daisuke lives a reclusive, withdrawn life. Daisuke has a childlike habit of biting his nails. Witnessing this one day, Eri worries he may be lacking affection, and one night she visits his room. This marks the beginning of a forbidden relationship between mother and son. As she touches her sons' bodies, Eri's emotions grow deeper, torn between maternal tenderness and emerging romantic desire, caught in a conflicted inner struggle.