Based on the erotic game by Jitaku Studio.

Our protagonist, Tooru Seo, writes down all the situations he fantasizes about in a notebook he calls his "sexual fetish diary". It's a form of self-pleasure that suppresses his overflowing sexual desire, and is an alternative to masturbation! He thought that no one would understand this hobby, and that he'd never be able to get a girlfriend. One day, Tooru forgot his notebook in the classroom and rushed back to get it, only to find his classmate, Chikage Ootori, masturbating with Tooru's sexual fetish diary in one hand. He suddenly finds himself in a harem situation, surrounded by heroines who accept and understand his sexual fetish, something he thought would never be accepted! And so his "real eroge situation" begins!! A girl who accepts all of the erotic situations that his fantasies, his special fetishes, overflow with. A sexy story where you can enjoy some intense sex with such a girl to the fullest!

(Source: PinkPineapple, translated)