You ask your girlfriend to turn into one of your family members to surprise your parents.

"Umm... Babe, can you turn into one of my family members to surprise my parents?" you ask your shapeshifting girlfriend.

"You want me to morph myself into one of your family members so you want me to surprise them? Teehee,... I like the sound of that, honey." your shapeshifting girlfriend replies as she's really like your idea. "Plus, if I turn myself into a man, or even someone old enough to be your mom or even your grandma, will you still have sex and love me?"

"Of course, I do, babe. And y'know, now that you saying, I well... really want to try some dark fantasy and a little bi-curious if you know what I mean." you replies.

"I know what you mean, hun. And tell you what, I think I'm not the only one who have a dirty thought like you." your girlfriend says as she's kissing you once more. "So anyway, which person in your family members I should be?"

"Anyone, plus I don't even know because I just hate thinking for too long." you answer.

"Okay, is that what you say, honey I won't mind about. Plus, could you check your anyone outside the house before I begin to morph myself." your shapeshifting girlfriend replies as you look outside and see there's nobody, not even your parents. As the area is clear, you thumb up and the your girlfriend use her shapeshifting power to change herself into a random person of your family members. With that, you sit back and watch your shapeshifting girlfriend's transformation.