Rinka, a wife, lives with her husband and father-in-law. Her father-in-law's dementia has progressed, and he has begun to urinate all over the room, becoming uncontrollable. However, one day while caring for him, Rinka witnesses her father-in-law's penis standing erect and powerfully erect. Unlike her husband who suffers from erectile dysfunction, Rinka can't help but touch her father-in-law's cock, which remains erect even in his old age... However, from then on, her father-in-law demands that Rinka satisfy his sexual needs at every opportunity! Oral sex is just the beginning. He even makes her caress his smelly and unsanitary anus, and in the end, he mercilessly thrusts his penis into her and ejaculates inside her. Although Rinka was initially unwilling, she gradually begins to feel pleasure from her affair with her father-in-law...