After retiring from his teaching career, Ryuutarou moved in with his son and daughter-in-law, content with his quiet daily life. But one night, as he listened intently to his daughter-in-law's seductive moans, Ryuutarou found himself secretly watching her through the door while she masturbated. When An realized he had seen her, and recalling that she hadn't had sex with her husband in over three years, she began to view her father-in-law as a new sexual target. Drawn to his deep sensuality and mature charm, the story leaves readers wondering how their forbidden relationship will unfold.