I did not know! Reveal the sister's secret!

This video is a game rip of the game "知らなかった!お姉ちゃんの秘密を明らかにする!" from studio GT-Four, which was released on December 1, 2017.

Mio found a strange diary of her twin sister. "What is this? Is this my photo? - No, it's my little sister... I never even guessed..."

In this diary, her sister kept a record of her sexual adventures and experiments with her boyfriend. She carefully wrote down every sexual experiment, adding additional photos. Of course, she first decided to master the technique of a blowjob, but of course she went through many trials and errors before she started to bring pleasure to her partner. Mio, unlike her sister, is completely inexperienced, so reading about how her sister gained experience was very interesting to her. However, suddenly her sister's boyfriend burst into the room, all excited and pounced on Mio, she didn't even have time to say anything...