Hot Summer Job/Get your sister into a 'custom' swimsuit
"If I have to wear a swimsuit I think it's only fair that you have to wear one too."
"Sure!" Bree cheerily replies, hopping off of the couch. You only barely manage to snag her by the arm before she can run away at full speed.
"Woah! Hold up! That's not the whole dare! Only part of it. Yes, you need a swimsuit. But it needs to be one you're okay with throwing away. Maybe an old suit you don't wear anymore."
"Oh, okay. I think I still have my teal one. It sorta still fits."
You approve of her suggestion with a single nod. "That'll work. Bring it down here so we can do the first part."
Bouncing with excitement, Bree hops across the room before stomping her way up the stairs exuberantly. You're not entirely sure where you're going with this yet, but you have an idea.
It takes a minute of searching but you manage to find what you're looking for in the bottom of a kitchen drawer. You head into the living room just as your sis bounds back down the stairs. She rushes over and hands you a plain little turquoise one-piece before jumping onto the couch, quickly adjusting her skirt after landing. It's only then she notices what else you're holding.
"You're going to cut it?"
"I was thinking about it," you reply, teasingly snapping mom's sewing shears a few times. They're really sharp and, since they're literally designed for this, make super clean cuts through all kinds of fabric. Mom imagines herself as a seamstress, but that just means lots of unused sewing junk can be found in weird places all throughout your house.
"But that's mine!" whines Bree.
"But you don't wear it, right? Isn't it old?" you ask. You spread open the small article, a bright plain blue-green sheet of lycra with two flimsy shoulder straps to hold it up. You remember your sister wearing this over summer vacation two years ago. It's definitely not her only suit, as evidenced by the fact that you're wearing half of a different one already. "You have others. I'm surprised mom hasn't thrown this away by now. It still fits?"
Bree fidgets a bit, looking down at her lap. "Not really, but.."
"Well it will fit better once I'm done with it!"
Turning the small swimsuit inside out, you expose the white lining that sits against your sister's skin and adds a second layer of fabric for comfort. This layer is sewn into the seams, but otherwise floats freely behind the colored body of the suit. Shears in hand, you carefully slice into the lining and then trace your way around the inside edges. It takes a good minute to do a rough cut all the way around. Having stripped out the gusset and protective lining, you turn your sister's small swimsuit into a monolayer of cheap lycra.
"There! You don't need that part. All it does is make it less stretchy."
"Oh! Really? So... now I can put it on?"
"That's the idea!"
You pass the thinned swimwear back to your sis who proceeds to step right into it in the middle of the living room. Being in a skirt (not to mention pantiless) certainly has a few minor advantages here. Bree pulls the one piece into place under her then shimmies out of the flowy fake skort, careful to pull it over the swimsuit now hanging off of her faint hips. With the skirt gone, your sis pulls the swimsuit higher, lifting her shirt up in the process. She quickly pulls her arms into her shirt and tugs the suit up under it. She begins to struggle a bit, the small one-piece and kid-sized top working in tandem to strangle her arms. But after a fair bit of squirming Bree pops her shirt off of her head and presents her now fully swimsuit clad body.
Bree throws her shirt away and her arms into the air. "Ta da!"
You stare a little too intently after your sister's reveal. The suit is definitely too small for her, digging into her shoulders and crotch equally well and bonding tightly to her torso. Having the lining stripped out does help her body look more defined, in the sense that even faint details and features - like her belly button, her two tiny nipples, and the contour of her yet-to-develop chest - can now shine through the otherwise opaque material. Along with that, she's sporting quite the camel toe, the taut swimsuit forming itself tightly to, and into, her modest little mound. You have to question whether you can even see the hood of her clit from here or if that's just a wrinkle in the fabric.
"It still feels tight," notes Bree, already picking out a wedgie.
"Yeah? Oh well. It was worth a try."
"I guess. So? What's next?"
"Next?" you parrot back.
"Yeah! You said this was the first part, remember? So what's the next part!"
You hadn't thought that far ahead. Really, the second part was her wearing it. You were mostly just curious how a one-piece would look without all that extra padding in the way. But there are certainly some intriguing options now.