"We sisters have become our big brother's personal pets." The sisters, Reina and Aina, fell in love with their step-brother, Shota, and at the same time, were thoroughly subjected to sex. The sisters completely fall for him as he indulges in perverted play regardless of the place... One day, Aina receives a love letter from another boy, and Shota becomes interested in another woman... Will the sisters' lewd relationship fall apart?