I ended up tutoring her sister, Ruka-chan. She's still a child, innocent and cute. She's naive about sex, accidentally flashing her panties or wearing a see-through bra. Despite knowing she's my girlfriend's sister, I can't help but see her as a woman. Before I knew it, I was kissing her soft, young lips. Shocked, Ruka-chan seemed confused by the situation. She didn't seem to mind. Is she this innocent? Realizing how wrong I am, my cock hardens.