HHKL-063 - Mistaken for my GF, I raw-dogged her nerdy twin sister from behind

My girlfriend has a nerdy, innocent twin sister who knows nothing about sex. One night, I mistook her for my girlfriend and raw-dogged her from behind! I kept going without realizing the switch, but when I finally found out, I panicked. Instead of being mad, the sister got turned on and started riding me herself! She turned into a total slut, way wilder than my girlfriend ever was. *This is a compilation from 'HUNTA-824', so please check your library before purchasing.