"Now for your transform, you will think of something really kinky that makes you really horny so you could transforms into whatever you do." you answered.
"Wait, what?" your girlfriend asked with her confused attitude. "So, if I think of something kinky, so that I could transform?"
"Well, yeah..." you replied.
"Okay, that's... really hard right now, hun." she responded as she's scratching her head. "I don't know what makes me think to something kinky."
"Well, try to think of something likes: dark fantasies or incest or bisexual or something like that." you explained to your girlfriend.
"Okay, that will do, hun." your girlfriend answered. "Well, let's try."
As your girlfriend concentrates her head, you saw her skin starts to shifted sensually, you realized that her transformation is worked. Plus you continue to watch your girlfriend to see what is she transforming into.