"It's necessary to draw a realistic erect cock!" My sister is an erotic manga artist. However, he doesn't seem to know about a man's body, so he always leaves his body to his assistant. However, since the assistant is only a virgin, I was called to my sister's apartment and my body is used as a reference! She was forced to get an erection, saying, "I want to see a real erection!", suddenly sucked, saying, "I want to see her face being given a blowjob!", and was stopped by saying, "I want to see her face looking like she's going to cum!", and finally made to have sex, saying, "I want to see her having sex!", and in the end she was left with the deadline...