With my wife hospitalized, her older sister Tsubaki came to help with housework. Though she's my sister-in-law, she's beautiful, kind-hearted, and always devoted to helping her brother-in-law. Drawn in by her warmth and tenderness, our intimate moments alone together gradually developed into a deeper relationship. Crossing the boundaries of our familial roles, we indulged in forbidden pleasure during these secret times while my wife was away. This hidden affair grows deeper, remaining a secret known only to the two of us.