Murakami is the eldest daughter in a family of two sisters, she pampers and loves her younger brother very much. However, perhaps the younger brother understands that he is the only son in the family, so his personality is very rebellious and stubborn. One day, when he suddenly dies, he takes his sister's phone and opens the photo album to masturbate. The older sister goes to find the phone and discovers her precious younger son doing something depraved. Instead of scolding, Murakami encourages him and lets him practice with a real person. In the following days, the two sisters are attached to each other, constantly committing incest everywhere in the house, despite the father accidentally catching them.