Keiji, the second son of a three-brother family, was always the low-maintenance child in the eyes of his mother, Sae. However, one spring, everything changed—his older brother began living alone after landing a job, his younger brother entered a boarding school, and their father was transferred for work, leaving the house suddenly quiet and empty. Sae was stunned by the shift, overwhelmed by loneliness and a deep sense of loss. Meanwhile, Keiji, haunted by years of living in his brothers' shadows, began to struggle internally with a growing desire to monopolize his mother's affection. As mother and son are left alone together, their days gradually spiral into a tangled intersection of forbidden emotions and escalating tension.