Little Sister (Patreon)

This is another anonymous caption commission. Hope you enjoy! Picture property of Brown-Bambi-Eyes, who doesn't seem to be active anymore.

Heidi knew it was wrong, but she couldn't help it - she was bored! Her housemate, Sarah, always got annoyed when Heidi went looking through her room, but Heidi had just been fired from her job, leaving her with plenty of long afternoons with Sarah gone, and nothing to do.

So how could she help but sneak a peek into Sarah's room, and then her closet? After all, knowing that the other girl didn't want her in there only made it more appealing, really... Why was she so adamant that Heidi stay out? She always claimed it was because she'd grown up as an only child, so she wasn't used to other people in her things, but Heidi suspected there was more to it.

Sure enough, it only took a little digging before she turned up something strange. It looked like a bodysuit, decorated in a rather childish pattern of ponies, and, even stranger, with snaps on the crotch. She'd seen a few that had those, though not many, and honestly, combined with the design, the whole thing looked more like a onesie, except sized for an adult.

Heidi giggled as she looked at the thing, glancing over at the clock to make sure Sarah wouldn't be home for a while longer. She stripped down to her bra and panties and pulled the thing over her head, snapping it closed and admiring herself in the mirror, snickering all the while. Seeing it on, it looked even more like a baby's onesie - the bottom was far bigger than she was used to, like it was meant to be covering a big, thick diaper. There was no way she wasn't going to tease Sarah about this when she got home, even if it earned her another lecture about minding her own business.

"Holy... Are you into this, too?" 

Heidi turned quickly, eyes widening as she saw Andrew, Sarah's boyfriend, standing in the bedroom door. She would never have admitted it to Sarah, but she thought he was hot... She had a feeling Sarah suspected as much, seeing as she always seemed to find some excuse to make sure Heidi and Andrew weren't in the same room alone for long... But this time, it looked like she'd failed.

"O-Of course," Heidi smiled, trying to look as seductive as she could manage in the ridiculous outfit, not sure what he was talking about, and not really caring. They were alone, Sarah wouldn't be home for a while... Anything could happen, if she just played along... "Even more than Sarah."

His eyes lit up. "Oh, that's perfect... She always said she saw you as a bratty little sister, but I bet she never expected this!" Heidi was a little taken aback, wondering if she should feel insulted by that, but before she could decide, Andrew took another step towards her, and her breath vanished in a gasp as he ran her hand across her crotch. "Just as I thought... Somebody isn't dressed appropriately, is she?"

A tingle raced up her spine. Was this really about to happen..? She'd fantasized, but she'd never thought... She knew she should stop him, but instead she gave an inticing giggle. "No, I'm not," she cooed sexily. "What are you going to do about it?"

"We're going to fix it," he promised, stepping past her and into the closet, pushing aside boxes and piles of clothes to pull out... a package of adult diapers. "Your big sister only needs these at night, but I bet you need them all the time, don't you?"

She was too shocked to say anything for a long moment, long enough for him to unsnap what she now realized actually was a onesie, to pull her panties down... But, unlike in her fantasies, it was only to diaper her... And then, later, after she begged him to let her use the bathroom, to spank her, and, when she tried again, to push something into her backside.

It had been bad enough toddling around in a diaper and onesie, following her crush like a little puppy dog, being given sippy cups of juice, having blankets thrown over the furniture, because she was "too little" to be trusted on it normally, being given a pacifier - and expected to use it - when she suggested she wouldn't mind sucking on something... Now, within minutes, she could feel her years of potty training fail her as she groaned, pushing her hands to her bottom, and the thick, crinkly padding there. 

Her cheeks burned as she felt Andrew's eyes on her. This was too much... It wasn't worth it. But it was too late... She knew there was no way she could make it to the bathroom now. Already, it was taking every fiber of her being to keep from pooping her pants, and if she tried to even stand up from her chair, that would be that. She should have known better, known that Andrew wouldn't betray Sarah, shouldn't have even tried to tempt him... Now, all she could do was turn around as the cramps overwhelmed her, as if she thought - like a baby - that not seeing something meant it wasn't there, and her diaper began to fill up with a thick, mushy mess.

Heidi barely even realized that, in her shock and mortification at what she was doing, she started sucking on the pacifier in earnest, not just because Andrew expected her to. She groaned, her nose wrinkling as she wiggled in her seat, the warm mass in her diaper squishing and squelching with every move, as if to make sure she didn't forget what she'd just done - as if she could.

"That was adorable!" Andrew gushed behind her. "Sarah says so, too... She loved the video!"

Heidi's cheeks were practically glowing at the thought of her roommate seeing her like this... "I-I'm going to go clean up..." she mumbled.

Andrew grabbed her arm as she tried to pass. "Sorry, sweetie, but Sarah says that she wants to be the first to give her new little sister a change, so you're going to sit back down and play until she gets home from work." He gave her lumpy bottom a firm pat, making her squeal and squirm, then stomp her foot unhappily. "Do it," he ordered, "Or I'll go get the paddle." 

Having already gotten a hand spanking, Heidi wasn't about to risk another, so she sank to the floor obediently, sucking on her pacifier as her bottom sank into her full diaper... She wondered how she was going to explain this to Sarah when she got home, if there was some way to word it without admitting what she'd been trying to do... Or if she was just going to have to keep playing along with this strange game the two of them apparently had.  Or did Sarah already suspect the truth, and that was why she was making her sit there in her messy diaper and play with her toys, like a naughty little toddler. Either way, Heidi had a bad feeling that Sarah wasn't going to let her out of this easily... And that her time as the "little sister" had only just begun.