When high school girl Mahiro goes to her best friend's house for the first time, she meets his mother, Shihori, who is good at painting. She is asked to be a model, and when she is called out, she is kissed while her best friend is out. At first she refuses, but she cannot forget the strange sensation she experienced, so she goes to see Shihori again. The two are entranced by their beautiful and forbidden relationship, which they cannot even tell their best friend about.