One Sunday, Ikumi's husband left home with their son, Susumu, because a horse they had become a fractional owner of was making its debut at the racetrack. Just as they were leaving, Ikumi's sex friend, Tadakazu, arrived at the house. Ikumi's crotch was already wet, thinking that she could have sex with Tadakazu without any worries until her husband returned. The two exchanged a passionate kiss without even exchanging greetings. From that moment on, their "unlimited fuck within the time limit" began...