Kyotaro Tsugumo, a university professor and medical doctor, is the director of the Sexuality Research Institute. One day, a female college student, Eiko Tsugawa, visits Tsugumo to sell her "sex equation" that she has invented. A few days later, Eiko and her friends, Yuki and Midori, are asked by the editor-in-chief of a recently banned weekly magazine to investigate the actual situation of soaplands