Living alone in my incredibly cramped apartment in Tokyo, I suddenly found myself sharing it with my sister (Kokoro). Kokoro, who had unexpectedly grown into a voluptuous figure, was always overly defenseless at home, constantly in a state of near exposure, leaving me at a loss for where to look. Unable to resist any longer, I forcefully attacked her and had sex with her without protection... But that night, she said, "I've been really aroused for a long time too..." and next, she asked me for unprotected sex! We've entered into a secret relationship that we can never tell our parents about...
