MIAA-300 Erina Oka's virgin brother takes his sister's provocation seriously and doesn't realize he's cumming, so he explodes with pistons.

Erina teased her unpopular younger brother as a joke. - The virgin younger brother took the joke seriously and misunderstood that she was inviting him, and immediately inserted his cock into her sister right after their parents left. - Erina climaxes with such force that her younger brother, who is not used to women, doesn't notice and continues to shake his hips. - The piston doesn't stop even after climaxing, causing her to climax over and over again, and she continues to be made to cum until her parents come home.