Shiori lives with her husband's family, forming a household of four with her father-in-law and brother-in-law. After deciding to divorce her husband due to his infidelity, she heads to the city office to pick up divorce papers—but on her way, an unexpected turn of events pulls her into a shocking situation. In the aging traditional house, she is forcibly subjected to anal training by her father-in-law and brother-in-law in various locations including the kitchen, living room, and hallways. Gradually, she begins to find more pleasure in her anus than her pussy, and abandons her plans for divorce, choosing instead the path of an anal slave. This story depicts Shiori's transformation and the shifting dynamics within her in-law family.