Satsuki Kirioka, the mother of three sons, always found her second son, Kenji, to be a low-maintenance child. But one spring, everything changed—her eldest son began living alone after landing a job, her youngest entered a boarding school, and her husband was transferred for work, leaving the household suddenly quiet. With the family home now empty, Satsuki began to feel lonely. Seeing his mother's loneliness, Kenji realized that, with his siblings gone, he had been receiving less attention. Driven by this, he began seeking to capture his mother's affection entirely for himself, leading them both into days of forbidden intimacy in the vacant family home.