After her husband's transfer left her in a sexless marriage, Reiko fell into a routine of late-night masturbation. One night, she accidentally caught sight of her son-in-law, Tetsuya, and his massive cock. Her heart raced, and unable to suppress her desires any longer, Reiko convinced herself, "As a mother, it's my duty to relieve him," sneaking into his room while her daughter slept. From that night on, her pent-up lust exploded. She repeatedly teased and played with Tetsuya's impressive shaft, indulging in pleasure right up to the brink, forging a thrilling new relationship between them.