When I asked my sister, who is famous as a slut in the local area, to let me have sex with her, she immediately refused, saying, "Absolutely not." I couldn't give up, so I negotiated with her, saying, "I don't mind if you keep your panties on, so let me rub my penis against her." Feeling sorry for her, my sister reluctantly agreed! I was so happy that I rubbed my dick against her panties, and of course it felt better than masturbating, so I ejaculated a lot! I thought, "Oh no, I'll get scolded," but when my sister saw the semen, her slut switch was turned on, and she took off her panties and asked, "Why don't you put it in?" and turned into a super slutty woman, asking for my dick!