Onii-chan no Seiheki, Watashi ga Mitsukete Ageru♪ ~Kyou kara Boku wa Imouto no Omocha~

"Hmm... So this is what you were doing, big brother..." The image on the computer monitor showed my sister in an indecent state. Well, it was a photoshopped image, but... I was masturbating while using my younger sister, as a sexual object. And then, of all things, she saw me in the most unwanted state. "Wow... You went to the trouble of making something like that and masturbating using your sister as material, big brother... Gross." My sister's scornful gaze and words... And then my sister hit me with the final blow. "What will happen if our mom hear about this? We might get kicked out of this house, big brother." "I'll do anything, so just don't tell our mom... Please let me off the hook this time." I pleaded with her with a bowing heart. "Hmm, you'll do anything for me... Then..." And so began my days of being at my sister's mercy...