Zzziiip...
You're barely one meter tall, and this shaggy doggy costume is still smaller than you. She- the costume- looks vaguely feminine, chocolate brown fur making her droopy ears look longer than they are. Somewhere in your old memories, the name "Shih Tzu" comes to mind. Still... it's a costume, right? And it has a mask, so nobody will be able to see you. This is nothing but an improvement.
Stepping into the costume... feels pretty nice, actually. Expecting the worst paid off in this case, because the inner lining of this costume is soft plush rather than the harsh confines conjured by your imagination. The soft doggie paws are nothing more than a pair of slippers, and the legs like a pair of fluffy snow pants. But when it goes past your hips...
"MMPH?" You look down and see that the tight costume is outlining your diaper. This does nothing to hide your problems, nothing at all.
Big Sis shrugs. "This is your second Halloween costume, Kim. I'm not getting another one." Your sister helps your arms into the sleeves, where- wait, what? There aren't even mittens at the ends of these sleeves, these are fingerless, useless bappers!
The mask settles around your face with a POOF. The plush lining squashes, and the muzzle leaves just enough space around your face to make room for the pacifier. With one more ZZZIIIP, you're 100% a dog.
You jump up and down a few times, enjoying the squishy feeling of the world around you. You barely even notice the loose red collar buckling around your neck until Big Sis clips a leash to it! You tug on the unwelcome addition and grumble behind the paci. "GRRMMN MMN..."
"Yeah, yeah, I'm not letting you wander off again. C'mon, let's go." Let's hope she's taking you some place good...