A high school boy is caught on his way home and bound outdoors with handcuffs. The key is tied to the boy's cock, and based on a tip that a pure, serious high school girl will come to help, the observation begins! Eventually, the serious high school girl comes to the rescue, but she struggles to retrieve the key, and the stimulation causes the cock to rapidly become erect! Though shy and unable to look directly at it, she gets excited by the erect cock. They end up having sex passionately until the sun goes down.