I was brought to a shy, climax-like state by my sister's boyfriend. (Minami Kojima, SONE-381)

Arosa, embarrassed by her younger boyfriend: I don't have a boyfriend, and my desires are unfulfilled... I overheard my sister having sex with her boyfriend, and the emptiness from masturbating was discovered. This shameful act, having sex with my sister's boyfriend, is so shameful... so embarrassing... so embarrassing... but it feels good. I don't want to betray my sister, but I can't suppress my desires... Having sex with a younger boyfriend is exciting, but I can't continue like this forever... So when my sister wasn't home, I decided to be embraced one last time...