Getting off the bus, you open the door to your house to find your girlfriend already there, nearly forgetting that she had your house keys as well as a backup. She rushes to you and embraces you in her open arms, then clasping your upper torso tightly. "Ah, sweetness, glad to see you again."
"Welcome back."
She then caresses your snout gently. Although a wave of joy flows through your body, you wonder if the wish has gone awry, and she's treating you like the dog you are (with more limbs, but still). "Why are you looking at me like that? You've always liked your chin being massaged like that." It's surprising you've forgotten all the times she had rubbed your chin.
"Let's head to your room. I have something to say, " you ordered.
"Sure."
In your room, you pick up the intact lamp to your girlfriend's eyes. "This is a wishing lamp with a genie inside. Make a wish, but please be very, very specific or it'll go awry."
"I've always wanted to become a part of you. Specifically, your asshole. It's been some time since this thought had began, but I don't know how this could come true, until this moment. Now I obviously need your consent for this, are you willing to let me become your sentient, talking rump?"
What kind of fantasy is this? Had she fantasized this aspect of you since you were human, or only after the wish had come true about you? The fact that shell be on the end of your lower torso does make things easier to bear as you won't be seeing her every time you bend down compared to if this wish was made as a human.
"Go ahead, but please be careful with your wish. How do you want to be treated by your family and friends? If you don't want to deal with that, how do you explain your absence?" The specificity of your wish at least evaded the glaring eyes of others, but you fear that she will suffer if she does not wish as properly as you do.
"I can deal with that, don't worry." She rubs the lamp confidently and begins to enunciate her wish even before the genie completely appeared. "I wish to become this dog taur's anus; yes, only the very end of the digestive tract, nothing else. I will retain my senses of sight (in the same direction as my opening will point), hearing, taste, smell and touch, except that I will find the expulsion of my owner's gas and solid waste pleasurable, even if it should taste and smell disgusting by all means. I will retain my capacity of speech, except during the expulsion processes, akin to the inability to speak while burping or with the mouth stuffed with food. My memories and capacity of thought shall also stay intact."
"I will be treated exactly like a body part and nothing more, and everyone else will remember me this way, except by my owner who will remember our relationship. I truly desire the full experience, up to and including having a thermometer stuck up my opening." You reactively flinch at the last sentence.
"Your wish is my command, however weird it is…"
"Now, for the transformation to proceed, you should sit with your rump on her, and your tail raised such that the hole is exposed." You do exactly that, and feel her asshole attached to yours. Overcome with curiosity, you turn around to witness her transformation into a part of you, the most intimate part in fact.
Her behind begins to meld into yours, her arms retracting into her body, her legs folding inside as well. At this stage she looks like a limbless torso. Gradually, her torso melds into your lower body, until only her head remains sticking out from below your tail.
Afterwards you stand up andwalk to the mirror to get a glimpse of her by bending your back end. Her mouth became puckered and her other facial features close up. Once the face completely sinks into your head, only the puckered mouth remains; she looks, and most importantly for a dog, smells indistinguishable from the orifice through which your waste will pass through.
Curious, you twitch your behind sideways a bit. "Hey!" You hear something speak from behind you. "Woah… This isn't kidding…" as the voice shifts to astonishment.
You suddenly feel some gas fill up your behind. "Sweetie, how much did the lamp co-"
PFFFFFFFFRRRRRRRRTTTTT! You let your gas rip from your girlfriend-turned-anus.
"…Oh gosh, that was exhilarating. Can't wait to do that again…"
Your tail flops down, covering her opening. "I can't see anything!" she proclaims in a surprised voice. Slightly fed up, you sit with your rump on the ground. "Oh, this floor is so cold!" she moaned.
"You said you want the full experience. You'll get used to this soon." Standing up, you walk to your bed and lay belly-up. You instinctively lick at your pucker to clean it.
"Ahhhhh… This is wonderful… fill me up with your slobber, please…"
You continue licking on her for a while. It's nearing midnight already, and you fell asleep nearly immediately. Will she regret this wish? Can the genie even undo previous wishes if so? That's another concern for a later time. You fall asleep.
"What stupid lovebirds," scoffs the genie, returning into his lamp.