Kanon, a female teacher, lives with her husband and his younger brother. Coincidentally, she also serves as the assistant homeroom teacher for her brother-in-law's class. One day, her brother-in-law expresses a wish to "know about a woman's body." Though hesitant, Kanon decides to fulfill his wish, providing sex education using her own body, both as his sister-in-law and as his teacher. However, before long, this sex education evolves into incestuous sex...