Up her ass

You decided to go through Kim's backdoor. Quickly formulating a plan, you shot towards her sofa and you waited for her to sit down. Since she's not wearing any panties, going up her asshole was easier when she was sitting on you.

Once she sat down, you slowly made your way towards her ass, then you rushed up her clean, shaven hole. As you went up further, you could feel your vision and sense of touch disappearing but before you could lose all your senses, you hear her gasp loudly and exclaim, "What the-". There was a brief moment where you felt like nothing, until...

"...fuck?", you say, your sister's last words coming of her (now, your) mouth. Soon, all of your senses returned as you adjusted to your older sister's body.

You are now in Kim's body.