You and your sister always trick-or-treated together, and she always got about 3x more despite going to the same places...they liked her more...

You and your sister were talking about what to do to get more candy...and she brought up the most random idea, you crossdressing, because she thought that it was because she was a cute girl, so a cute femboy would do the same...and she was right...

The next few Halloweens, you made the same amount of candy, maybe even more for both! Then, your sister gets a couples costume idea, monster handler and monster...and your sister bribed you for the role of monster handler...

You're wearing cute vampire wings, a frilly top that leaves little to nothing to the imagination, a short skirt, panties, thigh highs, and some latex heeled boots. Your sister is wearing a revealing monster tamer outfit that she got online, and she got your outfit just barely after she bribed you. She put you in a little thing to hold you around even though you're about an inch taller than her, and she just walked along, collect you two both candy. You wanted to get out, and you tried, but she stopped you

— Hey! You silly sissy vampire! I caught you and you have to stay in your cage!

She's really into character...this may have been the worst couples costume she could've picked...