Unaware transformation into dates Underwear

You had a date tonight and everything is going smoothly. He invites you back to his place for some kinky fun. He leaves to let you get on dressed when you strangely begin to transform. Your date comes back into the room and thinks you are hiding. He didn’t realise that you must have left him. The only thing you can find of you is underwear on the floor. Little does he know that you have transformed into them. He angrily put them on and takes to his bed to cum in them. He roughs them up while he masturbates. In the end, he cums all over you.