Yui was living a happy married life. Her husband was transferred for work, and he was to work at a place close to his parents' house, so they moved to her husband's parents' house until they could find a new place to live. Her husband has a younger brother who is a repeat student, and Yui, feeling that he is being treated badly by his family, decides to help him with his studies... However, her brother-in-law is attracted to Yui's body, and he bends in an unexpected direction... and bares his fangs at Yui...