My sister, a high school girl, has recently become very sexy and strangely tempting, but she's also a cheeky girl! For her birthday, I jokingly give her an "adult toy" as a present! She doesn't want it, but she's curious and secretly tries out the "adult toy," and my brother peeks at her and masturbates! Then, both of us get turned on in our erotic switches, and even though we know it's wrong, we can't help it and it develops into an unexpected incestuous fuck!