Discovering that his sister is practicing BJ in the toilet, the younger brother enthusiastically "helps" her to practice better (The film has 3 parts, the title is the first part of the film).
The older sisters were criticized by their boyfriends for not knowing how to have oral sex, so they took the initiative to practice with a water hose, fist the door, and... hang clothes. The younger brother saw his sister struggling but not effective, so he took the initiative to offer himself for his sister to practice better...
