Mitsuki teases her unpopular younger brother as a joke. - The virgin younger brother mistakenly thought that she was really inviting him and inserted his cock into her sister right after their parents left. - Mitsuki climaxes with such force that her younger brother, who is not used to women, doesn't notice and keeps shaking his hips. - The piston continues even after climaxing, and she is chased by the pleasure and climaxes repeatedly, continuing to cum until her parents come home. - "I'm already cumming!!" She completely ignores my older sister and makes her cum with the explosive piston!