[A younger brother helping his older sister with her graduation thesis. She is wearing casual loungewear with no bra] Even though we are brother and sister, I was so excited by my sister's defenseless appearance that I wondered if she was trying to seduce me! Even though I knew it was a lie, I just couldn't resist... What! Was she really inviting me? Before I knew it, she was asking me to do it, and I couldn't stop either... But it's dangerous! We're family after all! It's dangerous to cum inside! Crab-claw lock! ?