SONE-681 "She's too innocent to do what an older man tells her to do!?" I was attracted to my girlfriend's younger sister, so I secretly had sex with her. I'm such a terrible person.

I ended up teaching her younger sister, Ruka-chan. Even though she's a high school girl, she's still a child, innocent, and cute. She doesn't seem to have much knowledge about sex, and she flashes her panties and shows off her bra without any hesitation... Her breasts are big for her age. Even though I know she's my sister, I see her as a "woman". Before I knew it, I was kissing her young, soft lips. Ignoring Ruka-chan's surprise, I was passionately devouring her tongue. It was probably their first kiss. Perhaps because of her shallow knowledge of sex, she doesn't seem to understand the situation yet. She doesn't show any signs of reluctance... She's so innocent... My penis was erect enough to realize how terrible what I was doing was.