Mitsuki, the stepchild of remarried parents, is a serious, cute, and proud sister-in-law who is popular with everyone. - I was living a happy life having such a sister. - One day, my parents set out on a day trip in the morning. - I decided to spend the day alone with [Mitsuki]. - They were living their lives as usual, but when they were alone in the living room, Mitsuki, who was always cute, started acting strange. - He kissed me covered in saliva, showed me how he masturbated, came to wash his body in the bath, became extremely aggressive and came to steal my body... - Me, what should I do?