You're walking down the road when you see a little puppy crouched in an alleyway. It's a baby German Shepherd, with floppy ears not quite straight and paws too big for its body. You know you wouldn't be able to take it in, your poky apartment is no place for a dog that will grow up to run and hunt and protect. But, maybe, you think, if this gun can change reality, then this pup may have a better chance in the world as your girlfriend.
You aim the gun and fire. The beam hits the puppy in its chest and it whimpers as a change overtakes it. It begins to age rapidly, growing up before your eyes. As it does, you can hear the dog's bones cracking and reforming as it takes on an upright stance. The changes continue until you're looking at a very androgynous anthro dog.
You wait for its breasts to grow in, for it to become lovely and female as your perfect new girlfriend. But that doesn't happen. Instead, you watch as the dog's shoulders broaden. Its jawline sharpens and its chest grows wide and thick. It begins to stretch upward too, towering over you. A massive doggy cock makes itself known as it pokes out of its sheath. You stare in horror at the huge 6'8, muscular dog morph you've created.
"James? Why are you staring at me like that?" the dog asks. His voice is strangely quiet and timid. He stares down at you, still hulking even as he slouches to make himself smaller.
"Who are you?" you stammer.
He sighs. "Oh, please don't do this to me, James. I don't like you laughing at me." When you give no reply, he runs a paw down his face. "Fine. I'm Caleb, your boyfriend, remember?"
You shake your head. No, this gun was supposed to give you a girlfriend. But you realise with dawning horror that there must have been a reason it was in the bargain bin. And, with even more shock, you realise that you're kind of turned on by Caleb. That can't be true! But the more you think about women, the more you get turned off at the thought of fucking them.
Caleb, however, you can just imagine running your hands over his muscle-bound, furry pelt. Pushing him into bed, having him squirm beneath you as you plunge your cock into his ass. Having this beast submit to you like you know he wants to. You salivate at the thought. Standing back, you give Caleb a new appraisal.
Perhaps this is not what you wanted, but you could certainly make this work.