After her husband's death, stepmother Maki began letting her armpit hair grow. Her stepson, Nobuo, found himself increasingly aroused by her appearance. One day, Nobuo accidentally witnesses Maki engaged in intimate acts with his uncle, and Maki soon discovers that he saw everything. From that moment on, Maki begins teasing Nobuo, indulging even more deeply in carnal pleasures. Their relationship gradually intensifies, escalating into something new and forbidden.