My girlfriend, a busty girl who's bad at saying no, secretly gets aroused by my penis and becomes incredibly sensitive, capable of instant orgasms. (Nosaka Hiyori, SONE-655)

I recently started dating my girlfriend, and when I visited her house, I was introduced to her younger sister... Are they really sisters? Her personality, face, breasts (G-cup), sex life... her sister is better than my girlfriend in every way... I couldn't resist the urge to make my move! ...Eh! She's completely defenseless!? Because Nana is incredibly kind and obedient, unable to say no, we gradually crossed the line and a series of sexual encounters ensued. "No... my older sister is right here..." Seeing her sister's huge breasts exposed when she wore her school uniform made me lose control... I secretly used my penis to vigorously penetrate the underage girl! Enjoying the immoral feeling brought by the young and fragrant student's vagina, indulging in instant orgasms... I freely manipulated the submissive and sensitive little sister's vagina, making her reach orgasm multiple times!