The stepchildren Ichina and Imako used to live under the same roof, just like brother and sister. However, the intimacy of sex, which started with innocent interest, distorts the relationship between the two.

Imako is forced to take a synthetic drug by Ichina. She notices a change in her body due to the action of the drug. The feeling of excitement does not stop just by him stroking her head, and from there she accepts all of Ichina and continues to serve his body. When Imako notices the cause and protests to the dealer, Tatsuki. She is instead offered more drugs. Imako's body, which remembered the pleasure, could not reject Tatsuki and she could not stop her own runaway desire.