Kanon, a female teacher, lives with her husband and his younger brother. Coincidentally, she also serves as the assistant teacher for her stepbrother's class. One day, her stepbrother asks her to "learn about women's bodies." Kanon is confused, but in order to fulfill her stepbrother's wish, she uses her own body to teach him sex as both an older sister and a teacher. But before she knows it, that sex education turns into incestuous sex...