Cake-Flavored Helium

“Princess Luna,” a fellow guard speaks, “is it really true that Celestia has gone off on a vacation?” It has been only a few months since Celestia’s sudden departure.  It was a rather odd. She was here one day and vanished the next day. It certainly raised several alarms and nearly threw Canterlot into a state of panic. This was, however, resolved when Luna said that her sister had simply gone off on a break and that she would take over her duties of raising and lowering the sun. Though it does seem rather suspicious that only she knows this.
“Of course, my dear sister told me herself. She felt she has been working so much for her kingdom day after day without getting a long break,” Luna replies as she raises her foreleg. “You have to consider the time where she had to raise both the sun and moon during my punishment. Something like that would take up so much energy from her.” The guard, who asked the question, starts to feel sad as the thought of an exhausted Celestia appears in his mind.
“Y-You’re right, Princess Luna. I shall not question anymore. I do hope Celestia is fine..where ever she is,” the guard states before exiting the throne room. Luna smiles as she watches him exit, leaving her alone again. “Now for some peace and qui-,” she says before a nearby alarm goes off beside her. Using her magic, she quickly shuts it off and smirks.
“Looks like it is that time again,..” she whispers to herself, “time to pay my dear sister a visit.” Her wings slowly open as she hops and descend onto the floor. With a quick spark flash of light, she’s gone.
Just outside a nearby mountain range, another flash appears, Luna standing in the center of it. “If I remember correctly,” she says as she approaches one of the mountains,”it should be right around...here!” With a press of her hoof, part of the mountain sinks to the ground and reveals a hidden entrance. She moves forward into the cave.
Light taps of her shoes echoes throughout the cave, giving it a sense of emptiness. Luna hums calmly to herself. She wonders if she is going in the right direction until subtle sounds of hissing  begin to emit from within the cave. A smile spreads across her face. She’s getting closer to where she needs to be.
Soon, sounds of squeaking and groaning start to become audible. Smells of sweet, delicious cake begin to flow into Luna’s nostrils. She’s close. Up ahead, there is a  light revealing a rather huge, bloated object floating above the floor. It has a white, shiny texture that glistens in the light. A long muzzle slightly pokes out, smooshed between three orbs. It has a oxygen mask attached with hose that seem to be connected to a set of tanks. Above its snout, a messy, pastel colored mane sways to the side, a horn wearing a ring sticking out. On top, there are two comically, balloony shaped wings sticking out from it’s back. She trots closer to the bloated, squeaking object until she gets a clear view of its face.
The object has purple eyes that were half covered by its eyelids, making its expression look exhausted. Muffled pants emit from the mask. Luna grins widely before opening mouth to say, “I’m back, Sister!” Celestia’s eyes widen upon hearing her voice as her heavy pants quicken. She groans as she tries to move back, but there were ropes attached to her round, swollen hooves. She wiggles her covered snout, but her puffed cheeks and swollen chin were not making it easier to move it.  The princess of the night snickers at those attempts before moving under her huge tummy to give her puffed navel a teasing smack. It’s immediately reward with a muffled, loud moan  from the blimp.
 Luna trots around the hovering blimp of a sister and chuckles. “My… It’s only been a few days, and look at how much you grown… You’ll easily be confused for a blimp that belongs in a parade,” she teases while prodding Celestia’s swollen underbelly, “I can hardly remember the last time you were so slim and slender.” The celestial lets out a loud, muffled huff of slight disapproval. It only lasts a moment before she starts to subtly gulp the gas flowing through the mask. There is something oddly addicting about it that keeps her wanting to consume it so much.
Luna flies up to her face and gently rubs one of her cheeks, which is already bigger than her head. “I know you wish to not get any bigger, sister, but I know you can’t resist its taste… its smell.... We both know that you love cake so much,” She states, “ but what would happen if I were to apply that scent and flavor to a nice lifting gas called helium?” Chills run down Celestia’s bloated back as that question lingers in her mind. She really did not want to keep gulping so much helium, but the taste and smell... it’s so enticing!
“I don’t know why, but I find it rather adorable how you  constantly gulp down that helium… almost like a piggy,” Luna whispers into one of her puffed ears. “I remember that night when you fell for my trap. You were in your room, trying to sleep, until you smelt something in the air. Something sweet and sugary… You had to follow the trail and find out what it was. You sniffed and sniffed as you trotted out of your room until you found the source. What did you find? A small helium spewing out gas that smells like the treat you love so much. You were curious and wanted a taste of it so you placed your lips on that nozzle and drank some of it. My, you looked so cute sucking on like a thirsty filly. You were so caught up in that moment that you never realized your once, slim belly was billowing out.” Celestia glared at her, but her words were too true to ignore. How could she let herself end up like this?
Luna climbs to up to her back and sits next to on her inflated wings. With a hoof, she plays those swollen feathers like a harp. Celestia closes her eyes tightly and shudders from the odd pleasure of her wings being played with. “It was a slow progression, but you were already blowing up. Your flanks swelled out like two balloons with your legs thickening. Your chest started to puff out, getting close to the tank. So distracted… You didn’t even notice me putting that ring on your horn and using magic to hold your lips in place. After all, we can’t have balloons casting spells or trying to escape,” She says before pulling on a balloony feather and letting it snap back in place.
“Of course, you had to notice so late. Your belly is already pressing on the floor and magic keeps fizzing out of your horn as you try to shove the tank away… I honestly think I was lucky enough for all of this too work. You have no idea how hard it was to quietly move you here without your bloated rump squeaking up the night… Are you enjoying your helium, Sister?” Luna asks. Celestia closes her mouth tightly in an attempt to show resistance. She wants to show her sister that she can fight back her cravings.
Luna shakes her head before hopping off and flying towards the tanks. “Sister, you know this is just a light stream. If you think you can simply reject your meal, how about we turn things up?” Luna suggests. Her hooves quickly turns the valve, and Celestia is immediately assaulted with a huge blast of sweet helium. Her nose scrunches up as the scent fills her nostril. Beads of sweat drip from her forehead. Bits of drool seep from her lips. She can’t give in to her temptations.
“Now, now, Sister. I know it has been only a week since your disappearance. Surely, you have not lost your taste in sweets.” Luna comments,
Celestia’s mouth starts to water as her hunger starts to get the best of her. “Maybe...just..one..lick..” she thinks to herself before opening her maw a bit to let her tongue out. Sweet, sugary flavors coat her tongue. Her pupils start to shrink as a moment of regret fills her mind. She couldn’t resist any longer.
In mere seconds, Celestia starts to madly consume the gas. Her head thrashes left and right as muffled slurping sounds emit from the mask. Luna’s grin grows wide from her sisters immediate submission, but only for a few moments. She is bloating rapidly and filling the room faster than Luna had anticipated. She only prepared the room to have twice as much space as their bedrooms.  Thoughts of regret fill her mind as she takes some steps back from her blimp.
Space is starting to run low for her growing captive. As much as she dislikes the idea, she has to cut the flow. She attempts to move towards the valve, but suddenly feels something hold her back. Confused, she looks back and finds her culprit, her tail. It’s caught under her sister’s expanding gut. Panic starts to ensue as she vainly tries to grab the valve, but she’s only a mere inch from its side. Her view starts to darken as her sister grows bigger and pushes her towards the wall. Any attempts of trying push the princess balloon is only met with squeaks and her hooves bouncing off.  Soon, the white growing mass squished against Luna’s face as her back presses against the wall. Using all of her legs. She tries to make one last push to spare just a few more seconds. Beads of sweat drip from her head as her horn lightly glows. A magical aura wraps around and turns it back quickly.  Out of breath, her legs slide off her sister as her girth billows out just bit for it to smother her.
The hissing dies down slowly as the hose becomes empty.  Bits of fog and saliva stain Celestia’s mask. She licks around with hopes the flavored gas would come back on. Meanwhile, her sister grumbles and grunts due to the limited space between her and her blimp of a sister. Any slight movements she makes would only make the white balloon squeak, groan, and subtly moan. “Ugh…if you didn’t look so adorable while you consuming that helium, I would have never pushed you this far,” Luna mumbles. It seems she is going to need to find a new location for her balloon that offers plenty of room, though that is going to take some time. She starts to ponder for a moment on what to do with her sister during that time.
Luna remembers that Ponyville is planning to host a parade soon. Hopefully, they don’t mind an enormous Celestia floating around.