A naughty older sister who shows off her sex with her boyfriend even though she knows her younger brother is watching. She comes to where her younger brother is masturbating in the bathroom and starts handling his erect dick, saying "You have to peel it properly and wash it." She teaches him about the dick with her mouth, saying "I'll give you a sex education," makes him use toys in the room, and the younger brother's libido switch is turned on. Mao-chan, who was irrumatioed by her younger brother's excited erect dick and revealed her dom nature. Now, the older sister continues to be fucked so much that she convulses with her younger brother's oni piston and continues to scream.