With the "supplies" in tow, Twilight returned to Ponyville as she tried her best to keep a low profile. The nature of Cozy Glow's punishment had been kept vague to all but those closest to the filly, and Twilight wanted to keep it that way, especially since she was still trying to figure out who Cozy's parents were and why she'd gone behind their backs to attend the School of Friendship.

"I hope Cozy Glow's been behaving herself and hasn't given Spike and Starlight too much trouble." Twilight thought to herself as she made her way up the front steps of her castle and through the double doors. Only once she was safely on the other side did she allow herself to sigh, setting her saddlebags filled to the brim down.

As if on cue, Starlight appeared with a squirming Cozy Glow held in her magic. And Spike was walking behind while wearing gloves and carrying a toilet brush. "Good, you're home!" Starlight exclaimed with relief! "Cozy's been fussy all day."

Cozy just stuck out her tongue and blew a raspberry.

"Oh, she has, has she?" Twilight commented as she trotted forward with a frown. "Cozy, why are you still putting up so much of a fight? Don't you realize this is your punishment?"

The diapered filly only pouted. "I don't care, you poopy head! I'll find a way to break out of here sooner or later! I'd much sooner be thrown into Tartarus than spend another day with you."

Twilight only shook her head as she picked Cozy up. "I thought you would prefer something a little less extreme. I'm trying to help you by giving you a chance to fix your bad behavior before it's too late," Then she looked over the filly, inspecting her diaper and finding it clean. "Still dry, huh? You haven't had any accidents at all?"

"No, I did! That no good dragon of yours put laxatives in my food!" The filly pointed out! "And you won't believe what else he did! He used a magic plunger to flush me down the toilet, though to be honest I'd rather have stayed in the sewers than be treated like this."

Starlight replied. "It's true. And as punishment I'm having Spike clean every bathroom in the castle for a month," Then she added. "Aside from that though, Cozy only wet herself a little and hasn't done anything else. I keep telling her it's not healthy to hold it in but she just doesn't wanna listen."

Spike grumbled. "Are you absolutely sure this is the right choice, Twilight? Cozy doesn't seem to be getting any better. Even if what I did was wrong, I did it because I'm tired of her continuing to act like a brat."

The young alicorn wasn't convinced, she didn't want to admit Cozy was a lost cause. She'd once thought the same about so many other things and had been proven wrong, who was Twilight to decide that a filly no one really knew was an irredeemable monster without at least trying to understand what would motive her? "We've only just started the treatment. She's got until the end of the month at least to straighten out her behavior before Princess Celestia and Princess Luna show up," She explained. "Let's at least try to make it to there."

The little dragon just snorted. "Whatever. Just keep her away from me for both our sakes." And then he went away to resume his bathroom cleaning duties.

As for Starlight, she just yawned. "I think I'm gonna go lay down for a little while, Twilight. Plus, I need to get back to the school to see that things are getting back on track. I'm certainly going to have a lot of students who will need counseling after what Cozy did," She hoofed the filly over to Twilight. "You can take over for a while. Maybe you'll have better luck with her than I did." Then she trotted away, yawning again.

Twilight and Cozy were now left alone, and Twilight turned her attention first to her young charge and then to all the "supplies" she'd picked up from her parents. "I'm going to get some things set up in your nursery. I'll have to size them up a bit to fit you though seeing as you're kind of big."

"Because I'm not a foal!" Cozy roared in protest only to be ignored.

"Just stay out of trouble, okay?" Twilight pleaded. "And don't even think about trying to run away. I've set up a new alarm system that'll activate if you try to flee, so I'll know in an instant no matter when you might make another escape attempt."

The padded pegasus protested. "You're lying!" To prove her point she immediately tried to run to the door to open it, but as soon as she reached out a hoof to touch it there was a flash of magic and Twilight had appeared in front of her. "But that's not fair! I just can't win!"

The young alicorn cooed. "Oh, you can. The only winning move is to just give in and start cooperating. It's the only way you're ever going to be a big girl again. Besides, the diapers aren't coming off until I say so," And she warned. "You already got one strike on your potty chart. Don't make me add more."

Cozy only frowned and plopped down onto her rump, she was in no mood to cooperate with Twilight or anyone else.

Twilight smiled in satisfaction. "That's a good girl, Cozy. Sit there and think about how you'll improve on that bad attitude of yours. If you need me, you know where your nursery is. And don't be ashamed of using your diapers, they're there for a reason." And then she set off, picking up her saddle bags as she trotted to Cozy's nursery. "Maybe if Cozy got to play with some actual foals she might learn how to behave. I'm sure there are some that could teach her." She thought to herself.

The pegasus filly was not along for very long. She'd been sitting in the same spot for only a few minutes at best before she saw the castle doors swing open. Into the hallway trotted an earth pony filly with a dazzling magenta coat. She sported a diamond tiara similar to the one displayed for her cutie mark, had light grayish violet locks for a mane and tail (with white streaks shining throughout) and the most innocent cornflower blue eyes. In a lot of ways this filly reminded Cozy Glow of herself.

The headgear wearing filly soon cleared her throat, making herself known. "Hey, aren't you that filly they say tried to take over all of Equestria by draining it of magic? Not even in my bad girl days would I have thought of something like that."

Cozy, for her part, just blinked and tried to cover up her padding as she coldly replied. "What's it to you? You don't attend Princess Twilight's school, you weren't there when some of her students thwarted my perfect plan."

The earth pony filly just laughed and rolled her eyes. "Oh really? And what exactly did your plan involve after you'd successfully drained all the magic? Not that I mean to make a point, but size kind of makes a difference in confrontations. Without magic you wouldn't be able to fly, and almost anypony could knock you down if they wanted to," She then pointed out. "Not that I would ever do what you did, but if I did I'd at least have thought things out more carefully. Because it sounds to me like your plan wasn't much of a plan."

The pegasus filly just scoffed, thinking to herself. "Whatever, that wasn't my real plan." But out loud she only asked her visitor. "Why do you care?"

"Well, I just had to come and see for myself if the rumors were true," The headgear wearing filly declared. "Because it kind of reminded me of what I used to be..." A look of shame crossed her face and was reflected in her tone of voice before she perked right back up and said. "But that's all in the past, that's not the pony I am anymore. I'm Diamond Tiara by the way, and you are?"

"Cozy Glow." Cozy answered, still trying to keep her padding hidden from view.

Diamond nearly gasped in surprise! "No way! The same Cozy Glow the Cutie Mark Crusaders helped?"

"Oh, so you know those good for nothing fillies?" Cozy spat at the ground.

Diamond's eyes narrowed. "Hey, they're not 'good for nothing'! I owe them my new outlook on life, they really are the most amazing ponies ever!" Then she took notice of something that, despite being in plain sight, she hadn't thought much of even though Cozy wasn't doing a good job of hiding it. "Hey, how come you're wearing a diaper? I thought most ponies stopped wearing them by the time they were three, or at least that's when I had to give them up."

At that the little gears in Cozy's mind began to turn as she started scheming, thinking to herself. "She doesn't know about my punishment! Which means I can take advantage of her like I took advantage of this idiotic crusaders!" And with practiced precision she began to sniffle, putting on the same display she'd used on the Cutie Mark Crusaders. "You promise you won't laugh at me or call me names?"

Tiara shook her head. "That's something the old me would've done."

Still sniffling and pretending to cry, the pegasus filly whimpered. "I still wet the bed sometimes. So I have to wear diapers before bed or before naps. Everypony always made fun of me for it, calling me a stupid diaper baby and things like that."

The headgear wearing filly let out a gasp! "That's horrible! How could anypony do such a thing to you?!"

"Because someponies are just mean like that," Cozy whimpered. "I wanted to get back at them, and I thought the best way to do that was to bring them down to my level. I thought if I took away all the magic in Equestria, everypony would feel as weak and helpless as I do when I'm like this."

Tiara reached out a hoof to her fellow filly. "I'm sorry to hear that. If I were teased all the time over something like that, well I guess I'd be as nasty as you are regardless of whether it was the old me or the new me."

Then Cozy made a proposal as that scheming mind of hers prepared to lay her trap. "Do you think you could put on one of my diapers and play with me, just for a little while?"

Diamond blushed. "Well... I don't know. I haven't worn a diaper in years."

"Please? Just for me?" Cozy pleaded as her eyes grew wide. "I'll help you put it on and everything. It'll just be our little secret, okay?"

The filly with a dazzling magenta coat reluctantly agreed in spite of something inside her telling her to say no. "The Cutie Mark Crusaders would do it in a heartbeat. And I'm supposed to have turned over a new leaf." She thought to herself as she told her fellow filly. "Alright, you got a deal. But it's only this one time, got it? If anypony ever saw me with a diaper, I'd never live it down."

"Oh, is that so? Well that's unfortunate... for you." Cozy thought to herself as she fought back the urge to snicker. "Come on, I think Princess Twilight keeps a few of my spare diapers in the library." And with that she rose to her hooves, waddling along.

Tiara, suspecting nothing, followed close behind.

Sure enough, within the castle library was a small stash of strangely colored diapers (as opposed to the usual plain white kind). Cozy soon retrieved one of the purple colored ones with her mouth and offered it to her fellow filly. "Just lay down and put it on." She instructed.

Diamond did so, finding that the padding felt kind of... strange and yet also comfortable. It was surprisingly easy to slip it under her rump and pull it up so that it hugged her rear nice and tightly, her tail poking out through a hole in the back. "Never thought I'd be back in diapers again," She thought out loud. "Well, at least not until I was a really old pony."

Cozy used the thought as cover to snicker. "That's it, you fool! Now you're in my world! You'll never be able to use the bathroom again!" She thought to herself as her smile grew wide.

"So, what exactly do we do now?" Tiara questioned as she stood up and waddled over to her fellow padded pony.

"How about a game of hide and go seek?" The pegasus filly proposed. She would've recommended some foal toys, but all of them were currently in the nursery with Twilight (no doubt still working on sprucing up the nursery with those mysterious "supplies").

Diamond nodded. "That's a great idea! Why don't I go hide since you probably know this castle better than I do? Then we can swap roles for the next round."

Cozy Glow nodded back. "Sure, let's do it! Better go hide now, because I'm gonna start counting," And she put her hooves over her eyes, counting aloud. "One... two..."

The headgear wearing filly waddled her way out of the library to look for a place to hide. As she did so she became aware of an ever so faint twinge in her bladder. "I'm sure I can hold it in until this game's over. Then I can take off the diaper and ask Cozy Glow where the bathrooms are. I never said I'd use the diaper." She thought to herself. Even with her new outlook on life there were some things the former bully wouldn't do no matter what, going against her toilet training was one of them.

Cozy kept on counting, slowly reaching up to one hundred before finally lifting her hooves and quietly saying. "Ready or not, here I come!" She didn't really know where Diamond Tiara might be hiding and she didn't really care. All that mattered was drawing out the experience for as long as possible, to make sure she'd be around to witness the humiliation when Diamond would learn too late what made the diaper she was wearing special.

Sure enough, by the time the padded pegasus found her fellow padded pony, Diamond was greatly relieved. "Oh, thank goodness!" She declared, wiping the sweat from her brows. "Now, before we swap roles, can I take a bathroom break really quick? I mean, this castle has to have bathrooms somewhere, right? Who would ever build a castle without bathrooms?"

"You can't go!" Cozy protested! "Spike's cleaning all the bathrooms, you'll interrupt his work."

Tiara wasn't convinced. "I'm sure I can find one he hasn't touched yet. Besides, I really really have to go. I may have agreed to wear the diaper, but using it is out of the question! Rich ponies don't wet themselves!" Yet when she moved to try to take off her diaper, it happened! As soon as a magenta colored hoof made contact with one of the padding's tabs, it blew up like a balloon! "Hey, what gives?!" The filly shrieked!

The padded pegasus could hold back no longer, she dropped her sweet and innocent persona and started laughing. "Ha, welcome to my world! I don't actually wet the bed at all, I've been forced into wearing these stupid diapers as part of my punishment," Then she added. "And guess what, they've been enchanted so that only a grown-up can take them off. If a non grown-up tries, the padding inflates itself. So tough luck, you're gonna have to pee in your diapee like a helpless little foal!"

"Noooooooooo!" Diamond whined in protest, a protest that was in vain as her bladder could hold back no longer. An audible hiss could be heard as her already swelled up padding absorbed the contents of her bladder like a sponge. It only lasted a few seconds, but for the filly it might as well have been a lifetime.

Fortunately for the rich filly, help was soon on the scene in the form of Twilight. She had heard the cry and had come rushing, afraid of a disaster. What she saw made her heart sink.

Cozy Glow was displaying a smile of almost sadistic glee at having tricked another pony into one of her diapers. And meanwhile, a now humiliated Diamond Tiara was stuck in a swelled up and soggy diaper.

Twilight quickly moved to reduce the swelling in Diamond's diaper and then removed it, balling it up and tossing into the nearby trash. "I'm sorry about this, Diamond Tiara," And she told her guest. "There's a bathroom just down the hall from here, first door on your left. Why don't you go wash up while I deal with Cozy Glow?"

Diamond nodded and ran off, too embarrassed and ashamed to say anything other than. "Thank you, Princess Twilight."

Cozy soon stopped laughing as she was picked up by Twilight and held in front of the alicorn. "Cozy Glow, I can't believe you just did that! Have you really no shame?!"

The padded pegasus scoffed in reply. "It's your own fault for forcing me to wear these stupid things all the time! I just felt somepony else should experience the shame and humiliation I feel."

The young alicorn groaned in annoyance. "Cozy, why do you continue to do this? You know you're only making your punishment worse. At this rate you'll never get out of diapers," Then she turned the filly around and used her magic to pull down the diaper. "You know what's coming! Keep acting like a naughty foal and you'll be punished like one."

"Whatever! You're too soft to actually spank me! Even Spike was tougher on than you are!" Cozy growled in defiance. But her boast was soon proven to be premature when she felt a solid smack on her rump courtesy of the princess who held her. Two more quick swats soon followed, resulting in a rump that had soon reddened again. Now it was Cozy's turn to start crying, more so from the pain than anything else.

"I'm not bluffing, Cozy!" Twilight firmly protested as she pulled the filly's padding back up. "I don't want to give up on you. I really don't. But I can't help you if you refuse to help yourself. So you'd better start changing soon, otherwise it'll be too late. If you get thrown into Tartarus you'll never be able to escape."

The padded pegasus said nothing, but in her mind she was thinking. "Why does this princess care so much about me? She's not my mom!" Yet strangely, a part of her began to feel. "She's better than my actual mother. My real mom spanked me way more often, and my dad did too." She blinked and shook her head, wondering where that reflection had come from. Why did she care who was and wasn't her mother?

"Well, I think it's time for a certain naughty filly to take her nap," Twilight scolded as she carried Cozy to the nursery. "And from now on, I'm not letting you out of my sight. You clearly can't be trusted to behave yourself without a grown-up supervising you."