“We have become Onii-chan’s exclusive pets.” The sisters Rena and Aina, having both fallen mutually in love with their stepbrother Shota, had already accepted a certain kind of training. He indulges in perverted games anywhere without caring about anything, and the sisters completely fall into depravity… But one day, Aina receives a love letter from another boy, and Shota begins to take an interest in another woman… Will the relationship of the sex pet sisters be destroyed?