There's a WHATquestria?!

"Tia..." Luna nuzzled her sister, not sure what to say.

Celestia sighed out her nose, limp and quietly crying. "She must be hexed," she concluded. "Twilight would never treat me like this if she was in her right mind..."

"Her friends believe her story," Luna pointed out. "Do you believe they are hexed as well?"

"No," Celestia denied. "They are merely entertaining her delusion. We will give them their few days."

Luna hesitated. "Dear sister," she blinked at the ground uncertainly, "Is it possible she speaks the truth?"

"Don't be ridiculous, Luna, I'll dowse you too." Celestia sighed. "Parallel worlds eerily identical to ours, specific people with specific names and all, except themed on such... stupid things? Those are for comic books."

"I understand it is quite far-fetched, but --"

The two of them jumped as a swirling pink portal opened in the room and a familiar voice called out, alongside a series of terrifying roars. "Run-run-run-run-run --" and then Twilight Sparkle dove and tumbled out of the portal, scrambling to put herself right-side-up. "Close it, close it, close it!" she screamed at the portal, which vanished.

She sighed, got up unsteadily, and began to dust herself off, her eyes closed. "Sun and moon do my tits hurt," she said to no one in particular, then opened her eyes.

She froze, taking in Celestia's blank, tear-stained face and Luna's dumbfounded, wide-eyed stare, both focused on her colossal, still-wobbling tits, in their pretty pink bra with white hearts, the nipples poking slightly through the fabric.

"You two look normal!" Twilight sighed in relief. "Please tell me I'm in regular Equestria, that whoever is inhabiting my proper body is still in regular Equestria, and ideally, that she has already mentioned the enormous boobs she's lent me..."

Then her eyes went wide in realization. "C-Celestia! What happened?!"

Twilight descended down the many staircases of Canterlot, towards the jail cells, accompanied by the princesses and the wide-eyed stares of every single guard they passed.

When one of the most precious ponies in her world had started yelling at her in pain and rage, she'd been startled, scared to death, and then her heart burst in grief.

But then it all clicked together, and while she still felt horrible for her beloved teacher-god-mom, for the first time in days she felt completely at ease, especially with one of Fluttershy's bras holding her megaton bombs in some vague semblance of good behavior. Because finally, Twilight knew she was home, and she knew exactly what was going on, and she knew exactly how to fix it, if only she could make it past a confused, pained, angry sky-goddess.

She had already tried to explain to them that she'd just hopped through another six Equestrias trying to get to them - the last of these being Dragonstria, where everyone was a dragon, not just the dragons. The one she'd just escaped was Chrysalis.

Twilight was distinctly aware of Celestia's sorrow turning to a more fiery rage with each of these worlds she attempted to attest she had been in. Fortunately, Luna seemed convinced that there was, at least, a Tittyquestria; she couldn't remove her eyes from Twilight's bonkhonagahoogs.

"Tia, please --" Luna tried to soothe the big lady.

"I don't know what you're playing at here, Twilight," Celestia huffed, "Or how you've managed to... do that to yourself, but I've had enough of your mockery and your insolence. I didn't want to do this to you, but I'm going to have to put a magic inhibitor on you."

"I understand, Princess." Twilight sighed, only scowling slightly and shuddering as it was put on.

"Dear sister, please, if you'd just listen --"

"Quiet, Luna!" Celestia commanded. Luna paused in her step and leaned back, looking rather hurt.

"Luna, it's okay," Twilight assured her. "I'm not surprised that my counterpart upset her, I had a horrible experience in her world."

"Stop with these crude fantasies!" Celestia huffed. "Do you think I'm stupid?!"

"Never." Twilight smiled warmly at her, causing Celestia to hesitate. "We'll just go down to the prison and you two will see that there are two of me," Twilight reasoned gently. "There's no need to fight, I'll cooperate."

They opened the doors and walked in with her. "Oh wow, you put her in these cells..?" Twilight gasped.

"Wait, who's there?" came a second Twilight's voice from around the corner.

"There you are!" She chirped. Adjusting herself in her bra, she cantered around the bend, sighing with relief at the sight of her proper body. "What'd you do to get me thrown in jail?"

"... I greeted Celestia, um, in the Tittyquestrian fashion..." the prisoner meeped, twiddling her hooves and grimacing. "Oh, did Fluttershy make that for you?"

"You didn't!!" the burdened one sighed. "And yes, she did. I'm guessing you were going to check the royal library? I did the same. Your Princesses were practically competing to shove their udders the most boldly in my face..." She wrinkled her nose and put a wing over her face in distaste.

"That sounds like them..!" Inside Twilight giggled.

"I..." Celestia approached, looking between the two. "... I'm so sorry..." she managed, looking down in shame.

"Don't be," Outside Twilight walked over and nuzzled her. "If you'd gotten switched I'd think you'd lost your mind, too."

"I'm sorry I hurt you, Princess..." Inside Twilight warbled sincerely.

"I forgive you." Celestia returned awkwardly, looking away and fidgeting with her wings.

"I am lost on the details of what has happened..." Luna added.

Twilight walked back to the far side of the cell, discarding her bra as she turned back to them. "Need to let 'em breathe," she explained with a relieved sigh. Inside-Twilight nodded.

"You are... our Twilight in her body, yes?" Luna gestured between the two of them, blinking.

"Yes," Outside Twilight confirmed. "I woke up in her body, and she woke up in mine at the same time."

"And I still have no idea how that happened," Inside Twilight frowned. "I'm all ears."

"Half of you is tits." Outside Twilight snarked. "Anyway..." she grimaced. "I wouldn't believe a lick of this myself if I didn't just have to live through it, and in a week I'm gonna pretend this was a bad dream brought on by trying one of Pinkie Pie's experimental recipes too close to bed."

"Me too." Inside Twilight agreed.

"But," Outside Twilight continued, "I know what happened, and I know how to fix it, and..." She drooped and grimaced between Celestia and Luna. "And I'm sorry, girls."

"Sorry?" Celestia blinked. "Sorry for what?"

Twilight shrunk, lowering her head with a grimace. "Um, you two are not going to like this explanation. Especially you, Luna..."

"Especially..?" Luna blinked. "Why is that?"

"It's your fault." Outside Twilight grimaced.

"What!" Luna barked. "My fault..?!" She leaned back with a pale face.

Celestia smirked. "Oh? Tell us more..." she jabbed.

"Celestia," Twilight smiled apologetically at her and bowed her head, killing that smirk at once, "I'm so very sorry to drop this on you after what you've been through, but..." She looked at the corner and blushed. "Um, you and your counterpart are a dead ringer for one another..."

"Wha..?" Celestia blushed. "... Oh bother." she mumbled, hiding her face in her wings.

"... which is why I said those things..." Inside Twilight fidgeted with her hooves.

"Is she, now." Luna raised her chin warily, scowling. "And this is relevant because..?"

"Luna isn't," Twilight coughed delicately, "Yet both harbor feelings of resentment over the matter."

"Indeed?!" Luna abruptly stomped. "And how in the world does that cause this!" she huffed, gesturing between them again.

"Because..!" Inside Twilight suddenly piped up, catching on. "Luna is master of the World of Dreams, which is one across all worlds!"

"Yes." Outside Twilight nodded.

Luna blinked in shock, dropped her head, and nodded in resignation.

"Of course, visiting another world through the dream world is normally only temporary," Outside Twilight reminded everyone. "But there were... special circumstances." She yawned. "Oh, excuse me. Ahem. While our Luna dreams of being much larger, the other Luna sees it as futile and dreams of being more petite - if she is not going to exceed her sister, she may as well be a bit more mobile."

"I was quite spry myself before these grew in..." Celestia mumbled bashfully from behind her wings.

"But my Luna would be sacrificing her magic!" Inside Twilight pouted.

"Ponies don't always consider the downsides of their dreams." Outside Twilight reminded her.

She thought it over. "That's true, but..." Inside Twilight continued, "Are you saying this created a two-way-vacuum scenario? Shouldn't this have made Luna switch bodies?"

"I'm getting to that!" Outside Twilight stamped impatiently.

Inside Twilight's eyes spun to follow her wobbling tits. "Oh wow, is that what it looks like..." she blushed.

"I know we all know this, but sufficiently-in-tune dreamweavers unwittingly create a Tantabus when they are ashamed or afraid of something," Outside Twilight reminded. Luna nodded with an uncomfortable swallow. "And when two dreamweavers share regret or shame or fear over the same thing, they share a Tantabus Tandem, which is much more powerful and thankfully much more rare. But this was even beyond that power."

"Because the weavers were from different worlds..." Luna conjectured.

"Not just that," Outside Twilight raised a hoof. "If that was all, countless Lunas should have stirred every Equestria together with a super-Tantabus because of countless Nightmare Moons. But," she paused, her mouth fidgeting.

"But what." Luna narrowed her eyes. "Go on, Twilight Sparkle, tear my black heart right out why don't you."

"... that only happens with Titty Luna."

Luna shied back with a whinny. "I do not care for this moniker!"

"You're about to be furious!" Outside Twilight apologized, bowing her head, then sighed. "Are you ready for the stupidest part of this very stupid explanation..."

"No," Celestia admitted, peeking through her feathers. "But tell us anyway."

There was a pause heavier than the tits of a pregnant mare.

"... Titty Luna is the strongest Luna." Outside Twilight said to the ground.

"You dare!" Luna cried. "And how doth you figureth thatthth?!"

"Because Luna is the Princess of Dreams..." Outside Twilight sighed.

"And there are no stronger dreams than dreams of titty..!" Inside Twilight finished, hopping on her hooves in excitement to be connecting dots.

"That," Luna began blinking at the far wall. "That is fallen true and fresh from the back end of an ursa." She continued blinking.

"Hey, it's what it says in their royal library," Outside Twilight nodded with a scowl. "Titty Luna's unresolved Tantabus reached into another world - which, apparently, only hers can do - happened to pick our Luna's Tantabus to link with as opposed to any other's, and the Titty-powered Two-world Tantabus Tandem trolled around and traded two Twilights."

"Now I remember!" Inside Twilight perked up. "I had that weird dream! A big shadowy pony-thing sucked me up, I saw another me - I saw you! I forgot all about it as soon as I woke up..! Aw loons, I would totally have figured out that was a Tantabus if I'd friggin' remembered!"

"Yep," Outside Twilight nodded. "I forgot all about it too, until I started looking into..." She wrinkled her nose. "Uh, titty-dreams."

"But why us?" Inside Twilight tilted her head.

"I'm honestly not sure, but..." Outside Twilight reached down and awkwardly poked at her jugs, "I think the fact we both match our Lunas is a factor. Maybe it could've been Applejack. But not Celestia, or anyone else who wasn't vastly incongruent between the worlds."

Luna stomped, making everyone jump. "My frustration with my tits is more powerful than my grief over betraying Equestria and breaking my sister's heeeaaaart?!" she roared.

"Yep!" Outside Twilight nodded with a grimace. "Stupid, isn't it? But I have good news!"

"Well, by all means," Luna growled to the floor. "Could daffodilling use some."

"I've talked with Titty Luna about it, and she realizes that it's silly for her to feel inadequate. The only mares in Tittyquestria bigger than her are Celestia, Chrysalis, and Cadance."

"Cadance..?!" Celestia choked out a laugh, then covered her mouth, ashamed. "E-excuse me."

"So Titty Luna is working on her self-esteem," Outside Twilight continued, "... and dissolving her Tantabus, which should stop any more swaps, even if every other Luna in every Equestria stays insecure about her boob size."

Luna groaned and hid her face.

"And," Twilight continued, "So long as Titty Starlight is able to make another portal so Titty Twilight can go back, the swap itself is super easy to fix!"

"... Oh!" Inside Twilight gasped after a second. "Yes, of course! Now that you're here, it should be easy!"

"Let her out, please." Outside Twilight smiled. "And um, take this off my head, or her head, if you would..."

"Of course," Celestia mumbled, and briefly suffocated Twilight with her wings, popping the inhibitor off after a few seconds. Luna gave a control phrase with her magic to open the cell door, and the imprisoned Twilight walked out.

She immediately reached over and touched the big purple boobs. Their bodies suddenly lurched upwards, and then the two of them collapsed onto their bellies.

Slap.

"OOOUUGGHH..!!" Titty Twilight groaned. "O-oooh there's that old familiar feeeliiingg..!" She cradled her boobs with her wings and cried. Celestia hissed, her own wings lowering to protect herself.

Prime Twilight got to her feet and sighed. "Oh gosh, that feels so much betterHACK!" She clutched at her chest and coughed. "Why does breathing hurt."

"Forgive me," Luna grimaced, "I was enraged by her treatment of Celestia... S-so, you only needed physical contact?" She blinked, awkwardly brushing at her hair with a hoof.

"All boob-stealing magic is reversed if the rightful owner can touch the stolen boobs," Prime Twilight explained, regaining control of her breath. "Stealing her entire body is stealing her boobs, so it was canceled on touch."

"So if I ever offload these onto someone, I need to stay far away..." Celestia sighed.

"And be sure she treats 'em nice," Titty Twilight cut in from the floor. "Unless you swap your whole body, you'll feel any pain inflicted on them, not her."

Celestia said nothing, but her open mouth and furrowed brows said Can I catch a break here?!

"I think," Prime Twilight suggested hesitantly, "We should get Titty Fluttershy to make our Celestia a bra."

This got everyone to laugh, even Celestia, hiding her face again. "I would honestly give it a shot," she conceded.

"I've actually taught your Rarity the basics, she'll likely start a trend," Titty Twilight pointed out, then winced. "I'm so glad to have you back, girls," she sobbed. "You hurt so good." She winced up at Prime Twilight. "Did you let someone use me as boxing practice or something..? They ache a lot..."

"Um," Prime Twilight grimaced. "Theeeey almost exploded..?"

Celestia paled and swayed on the spot, reaching one wing up to her forehead unsteadily.

"Oh!" Titty Twilight laughed, getting back to her hooves. "Are you talking about the Cowlicorn Carcanet? Loons, do you think we'd just keep that sitting around if it did that? It's completely psychoactive. It doesn't change your boobs or give you any new power at all, but you perceive, uh, well, your tits exploding horribly." She cleared her throat. "Right, uh, it punishes mares for their pride and gluttony and makes them appreciate what they have. The Princesses have both worn it before, and so has Trixie."

"Trixie went through that..?" Prime Twilight furrowed her brows. So it really is their Alicorn Amulet...

"Oh yeah, Trixie was traumatized..." Titty Twilight frowned in sympathy. "But physically, she was fine. All the rest of us saw was an even worse attitude, we had no idea why she started freaking out."

"That's a relief!" Prime Twilight and Celestia sighed together.

But then Celestia frowned. "The other me was foolish enough to don such a thing?"

"Fortunately 'twas only an illusion," Luna grumbled, "Else would have rendered all of Canterlot a ground zero."

Celestia gave her an uncomfortable sidelong glare.

"Thy tits are weapons of mass destruction," Luna spat as Celestia's face reddened, "Even as blunt instruments they can seat giants and topple fortresses. You knocked a whole tower down in our old castle! If thy milk was ord'nance we could drop thee from an airship to annihilate a country and its neighbor, one per boob as the wind spread them out!"

"Oh!!" Prime Twilight remembered. "Titty Starlight should have that portal open again any minute now... I'm not sure where exactly she'll open it... but I need to tell you one last thing." She put a hoof gently on Titty Twilight's shoulder.

"What is it..?" she tilted her head.

"Please be good to Spike," Prime Twilight requested with a sad smile. "He's going through some tough times. Adolescent boy surrounded by beautiful, very coquettish mares. He never spoke bad of you, but I think he feels like you don't respect him. He's not just some pervert, okay? He's your little brother. Please treat him kindly and try not to make things uncomfortable and awkward for him."

Titty Twilight's eyes widened, then she looked down and sniffed. "You're right," she nodded. "We've been really inconsiderate. Thank you. I will. Oh, and I have a message for you, too!"

"What's that?" Prime Twilight blinked.

"Please be gentle if you ever critique Rarity's spellwork," Titty Twilight grimaced. "She's terrified you'll rip her apart."

"Oh!" Prime Twilight blanched. "Gosh, that explains everything! I was wondering if she was suddenly cutting off her magic when she knew I was around... Oh, and uh, your Spike's already fuffed Applejack..."

Starlight's portal swirled into existence.

"... not Rarity?" Titty Twilight asked after a moment, her head tilted in doubt.