“Shuntarou is a siscon with three younger sisters, Ayaka, Chiaki, and Fuyuno. His sisters despise him, and verbally abuse him every chance they get, so he wishes he had a gentle older sister.
One day, Shuntarou receives a mysterious email about a new erotic game called “”The Big Sister Experience.”” He starts to download the game, but it takes too long to load. Eventually, he gives up and goes to sleep. The next day, he wakes up as a shouta!
His sisters are confused, and Shuntarou makes up an excuse saying he is Shuntarou’s friend named Koharu who was staying over. All of a sudden, Shuntarou’s sisters start being really nice to him, and eventually, they start going “”out of bounds”” with him.”