Ten years ago, when Rin married their father, adult brothers Tatsuya and Kazuya were cheerful and sociable. After Tatsuya failed an entrance exam, he became a shut-in, and Kazuya gradually grew withdrawn and twisted as well. One day, Kazuya stares at Rin with clouded eyes and demands that she relieve him sexually. Afraid of what he might do, she gives in and comforts him, only for Tatsuya to catch them. Now both adult sons know what their mother has done, and her role as their sexual outlet begins.