After discovering her husband's infidelity, the sister-in-law, neglected and starved for attention, turns her gaze to her husband's younger brother, who frequently visits. Tempting him, she whispers, "It's okay... I have Seiji-kun now." As the brothers' relationship begins to unravel, she is consumed by newfound emotions—where will this forbidden romance lead? A mature tale of desire and love unfolding within a tangled web of human relationships.