My parents remarried and my new sister treats me like a kid because of my appearance, which makes me look younger than her. I always find her annoying because she's a real gal and a flashy girl. My sister, who is into tanning, always orders me to apply aftercare oil when she comes back from the salon. I reluctantly listened to her, but I started to get aroused by her body getting wet and shiny after applying the oil... My sister, who thinks of me as a worthless child, doesn't seem to suspect anything when I touch her sensitive parts. So I decided to give her an erotic massage, partly as revenge against her for always using me like a gal.