Your Friend's Sister is Hulking Out (Patreon)

You're spending the night at your friend's house. His cute sister is in town for a visit and also staying with him. Unbeknownst to you, she always had a crush on you. When your friend went to sleep, his sister knocked on your door. The next thing you know, the two of you were making out. Suddenly, she stops and says, "Don't freak out... I'm about to change."