One day, Itsuki, who had lost her house key, felt the urge to urinate at the entrance. She then asked her neighbor Imaoka to borrow his toilet but failed to make it in time and wet herself at the entrance. As Itsuki apologized, Imaoka, who had been lusting after her voluptuous body all along, used the secret of her incontinence to torment her… Imaoka became interested in Itsuki's sensitive reactions to anal stimulation and mercilessly penetrated her anus. The sensation, which she could not experience with her vagina, was deeply etched into her mind. And then again, Itsuki visited Imaoka's house…
