Reminder that these characters are 18+ in this story.
Another reminder is that the fanfic will feature Body Inflation, Sexual Content, Brief Nudity, and Non-Fatal Popping
Turn back if you are not comfortable with the subject matter.
Yuuki Mishima and Shiho Suzui were what you could describe as troubled, both having been abused by their former gym teacher, Suguru Kamoshida. However, that was some time ago, Kamoshida had his heart changed by the Phantom Thieves of Hearts, ridding them of the predator and they had long since moved past their trauma after that. Now, Mishima was known as the guy who ran the Phan-Site while Shiho was known as one of Shujin's star volleyball players.  While that was what they'd be known for, if there was one thing that their peers wouldn't expect to learn, it was that the two shared an inflation fetish.


When they weren't around others, the two were looking up various pictures of people inflating themselves, inflation art, and occasionally using a tank of helium or air to pump themselves up in private. The last part was something that shouldn’t be possible, however due to them having some minor interactions with the Metaverse, the means used by the Phantom Thieves to change hearts, they could actually engage in the practice. They enjoyed it and nobody exactly knew of their fetish, not even they knew of the other sharing such a fetish, that was until now.


Mishima was out buying himself a tank of helium, he was going to inflate himself real big. It was something that he was wanting to do for a while. Usually he'd inflate himself to become as wide as he was tall and to be touching the ceiling. This time he was wanting to grow to the size of a mountain. Sure it was pretty likely he'd end up letting others know what shit he's into but he didn't exactly care about that no more, since he'd just go in his gym uniform, something usually worn by everyone at Shujin.


As he was going up to buy the tank of helium, he ran into his classmate. Shiho. What she was holding was really unexpected. Just like him, she held a tank of helium as well, and she too did not expect to see him with one as well. They both stared at each other, surprised to see each other holding a tank. Eventually, Mishima was the first to break the silence asking, "So... you're into this too?"


Shiho, knowing what he was referring to, nodded to let him know that yes, she had the same fetish as him. "You want to talk about it later?" she asked.


"Sure." Mishima answered, Shiho noticed that he had a bit of a blush on his face, as if he was embarrassed about someone he knew knowing about his fetish. She shared the same sentiment as well. What they were into wasn't considered exactly normal, so it was a surprise to learn that someone they knew very well had the same fetish as them. The two went separately to make their purchases.


A few hours later...


Mishima had opened the door to see Shiho waiting outside. His parents weren't home so he didn't have to introduce her to them. Letting her into his room, she sat down as Mishima started talking. "So... you want to know about me... being into inflation?" he asked.


"Sure." answered Shiho who was more willing to talk about this considering that it was just her and Mishima. "Look Mishima, it's just us. Don't be afraid to not just fumble a few words."


With Shiho's reminder, Mishima didn't hesitate to start explaining. “I just stumbled upon some inflation art by accident! It was while I was running the Phan-Site! Initially I just ignored it but something about the art… it just made me want to see more of it. Then it led to me trying to see if I could inflate myself… and I loved it. So I’ve been doing it to myself ever since.”


“Huh… that's like how I got that fetish.” Shiho replied. “One accidental click and I just found myself sneaking tanks and puffing up when I was alone at home.”


“Does Ann know?” Mishima asked.


“No, she doesn’t.” Shiho answered. “She’d probably worry about me popping considering that… you know…” 


“Don’t remind me…” Mishima replied back, shuddering at the thought of what would’ve happened were it not for the formation of the Phantom Thieves.


“When I first discovered the fetish, I didn’t really have as much time to myself considering my parents were wanting to keep me safe. Had a hard time convincing them to let me stay at Shujin. Made it all the more nice when I could puff up in privacy.” Shiho explained further.


“Funny you mentioned privacy…” Mishima said. “I was wanting to inflate myself the size of a mountain.”


“But you’d have to be out for everyone to see…” Shiho responded. 


“I know, it’s why I’d be using my gym clothes.” Mishima said in response to the point Shiho brought up. “Makes it harder to be identified.”


“In that case, could I join you?” Shiho asked and was met by Mishima’s face going red.


“S-Sure!” he said. Shiho smiled. Given the blush on his face and the way he answered, he definitely liked her. 


“Thank you, Yuuki.” Shiho spoke. “Guess we’ll be a pair of airheads, just floating above Shujin. Maybe a pair of moons even…” she had stated the last part in a flirtatious manner, causing Mishima to turn a bit more red, making her giggle. “This was getting good.” she thought.


“I’ll just let you know that we’ll have to meet on the rooftop though.” Mishima spoke up, having regained his composure. “I-”


“I don’t mind at all!” Shiho interrupted. “That was in the past.” The idea of inflating alongside Mishima to gargantuan sizes was too good to pass up. For she definitely liked Mishima back, having got to know him more when their P.E. Teacher was out of the picture, he was a nice guy that she found cute. Him getting drunk on power when running the Phan-Site notwithstanding.
“Sounds like a plan then.” Mishima remarked with excitement.


“Maybe we could do a puff kiss as well…” Shiho suggested.


“That too then…” Mishima replied with a blush.


A few days later…


Shiho has arrived just as Mishima expected. Clad in her white and red gym shirt and shorts like he was. They were looking at the helium tanks they managed to sneak in. Mishima claimed the tanks would be for the school festival when asked by anyone curious. With everyone else in the midst of their classes, the two went off claiming to need to use the bathroom. They had the roof to themselves. 


“You ready?” Mishima asked, clearly excited to try this out with his crush.


“Sure am!” Shiho answered confidently, just as excited to do this with him. Both took out a tube they brought along, connecting them to their tanks as per standard procedure when they indulged their fetish. They stuck the hose into their pants, where they shoved it into their butts. While they could’ve stuck it in their mouths, they wouldn’t be able to do the puff kiss like Shiho brought up so they went with the other best option. It helped that shoving it in the posterior felt good, with the pair groaning in the small bit of bliss felt from doing so. All that was left to do is turn the valves on and let the fun begin.


“Ahh…” Mishima sighed in bliss after turning the valve on his tank. He felt the helium going up the butt and a small bit of pressure started to be felt. He and Shiho welcomed the pressure immediately for it wasn’t painful at all. Having inflated themselves before, they already knew that it was a pleasant kind, one that gave the two a tingling sensation.


Shiho was delighted to feel a bit of tightness start to form under her clothes, feeling her belly start to bulge out against gym attire, she rubbed it as it grew more, biting her lips as well. She took notice of Mishima’s jacket being unzipped. Doing so showed off a bit of the pretty boy’s belly already and she was starting to like what she saw, even drooling a bit. However she noticed her own stomach wasn’t as wide as his given that she zipped up her jacket. Unzipping it, she felt her belly bulge to catch up in size triggering a moan from her. 


It was obvious that both were having a good time at this point and Mishima was rubbing his belly down when he looked over at Shiho and saw she caught up with him in terms of belly size. At this point their bellies were mostly revealed and the size of them looked as though they had swallowed a huge watermelon. Blushing a bit when seeing Shiho wink at him, Mishima was taken by surprise when she playfully bumped her own belly into his, sending pleasurable  vibrations across both, and making him fall down on his own butt. Upon landing, Mishima moaned once more, feeling vibrations across each cheek. Looking behind, he saw his butt start to blow up as well. He looked to see it happen to Shiho as well who sat down and bounced on her ballooning buttocks with her expression looking to show her basking in how great it felt. “Always liked when it got to this part, Mishima.” she said. 


“I know, right?” Mishima responded. “How we all get sensitive and lighter. It’s always the best part of doing this.” Feeling his thighs expand along his now basket size butt, he moaned as he continued to bounce on it. He felt a bulge against the front of his pants start rising up before noticing how he and Shiho’s own bellies start to meld with the lower area. Feeling his belly caused a squeal of enjoyment from him. Such an act being made beyond easy because of it being large enough to look as though he ate one of his classmates and his gym clothes being unable to cover any of it.


With Shiho, she squeezed her similarly sized stomach, moaning as well. Her mind was bouncing, it felt amazing as always and she didn’t care about the fact that she and Mishima could get caught, nor could she care that the two were about to float up into the air. Feeling her feet start to sink into her inflating legs as well, she knew what would come next. 




Their teardrop shaped lower areas had gotten as wide as say… one of those King Frost shadows the Phantom Thieves had fought to make a comparison. Their pants weren’t doing well, rips starting to form across them caused by the widening rumps. Their shirts were more lucky, simply rising up from their wide bellies, however it wouldn’t be the case for much longer.


A groan came out of Shiho when she felt helium going into her breast area. Immediately after, she felt it growing against her shirt. Very quickly she gained a bust that put her best friend’s own to shame. Along with that, her backside started rounding out, stretching her shirt and jacket. Shoulders lost any definition as her arms were growing which made it stick out like a cone alongside her legs. This put an end to being able to feel herself but it wasn’t like she cared at this point. The pleasant pressure had grown with her and the tingling feelings were the perfect substitute. Looking over to Mishima, she saw that his body was in a similar shape. His belly stuck out a bit, looking bigger than her own and along with the bulge that made her drool, he had his pecs puffing up as well. Not as much as hers which had now become as big as a desk but still enough to be a bigger bust than Ann’s. Floating closer to the balloon boy, she buried herself in Mishima’s manboobs. She could hear his moans from doing so and moaned as well. The collision of the students sent a lot of pleasurable ripples between them. Eventually the pair were interrupted by feeling that the rest of their backsides had finished melding with their torso. They were now in a mostly spherical shape. 


Feeling Shiho move back from his moobs, Mishima could see that they had long since floated away from Shujin. In fact, they looked to be as big as a house. Surprisingly enough, their clothes hadn’t gained any more rips. Odd seeing as they were all struggling to contain the orb that were their bodies. Before he or Shiho could ponder about it more, rips started forming across the jersey, jacket, and pants again, as if to catch up on lost time. “Huh… why didn’t tha-oh god it feels great!” Mishima’s coherent thought was interrupted by the cold air ticking his body. With such a giant body came sensitive skin, already evident by when he moaned from Shiho colliding with his massive moobs but with more skin being exposed to the cold air above, he and Shiho would be having a harder time thinking. As more and more rips formed across their clothing, Mishima and Shiho started moaning, their bodies growing from the size of a house to them starting to get to the size of a two story building. Their chest area could be comparable to a single railroad car and Mishima’s belly stuck out, looking like he could contain several Shujin students. Inflating in the privacy of their room felt good but the Phan-Site Operator and the volleyball player were in ecstasy from feeling the cold air along with the pressure within. 


By now, they have long since gotten to the size of the Shujin Academy itself. Their moans still occurred but their minds were starting to think coherently again,maybe their bodies got used to the sensations. “Fuck! This is so good!” Shiho thought to herself. “Ann probably knows by now. Maybe I could get her and Ryuji to join me.” she said out loud. Despite being able to think coherently again, Shiho was still feeling rather horny. 


“Just Ann and Ryuji?” Mishima excitedly laughed. “You’re not thinking big enough! Let’s get the rest of the Phantom Thieves!” 


The mere suggestion made Shiho drool at the thought. Ann and Ryuji would be good looking as balloons and the rest of the Phantom Thieves were nice to be around but just the thought of the Thieves as blimps were a sight that they didn’t know they wanted till now. There was their dashing leader, Ren, his lucky love, Sumire, the painting himbo, Yusuke, the cute hacker, Futaba, the fluffy haired Haru, and the former student council president, Makoto. Just thinking of them as balloons was good enough to distract from her and Mishima paying attention to the fact they were starting to slow down in growth. Their clothes were surprisingly still on but seriously at their limits. Their undergarments were practically out for all to see, surprisingly having adapted to the swelling far better than the gym clothes.


A while later, as they floated about, Mishima suddenly felt that something was off. Immediately he realized that his helium tank was empty. He didn’t feel any helium going into him. Did his tank empty out or did someone disconnect the hose? Either way, he wasn’t growing anymore. “Shiho… have you noticed that nothing much has changed?”


“Why yes. I guess we emptied out the helium tanks.” Shiho answered. Despite the fact that they ran out of helium, she had seen enough images when browsing to know what must be done to start growing again. Without a word, she floated over to Mishima.


Mishima saw Shiho approaching him, a moan from both upon collision. “Shiho-ah! What are you doing-hng!?” 


“You mentioned wanting to get as big as a mountain right?” Shiho said with lust in her voice.


“Yeah…” Mishima replied. He was wondering what Shiho had been getting at.


“I was thinking this could help us get much bigger…” Shiho explained before puckering up her lips and going in to give Mishima a kiss. A puff kiss to be more specific. 


Mishima blushed from the thought of a kiss from Shiho. He also felt confused for a bit until the realization of what the girl intended, in which case his face turned completely red as he went in to kiss Shiho. Immediately upon their lips locking, Mishima and Shiho blew into each other, and just as quickly they started growing again. What remained of their clothes ripped apart into scraps, leaving the two completely in their undergarments. They moaned once more as they felt their exposed skin stretch even further as they continued to grow. They started to cover more of Tokyo. One by one they were covering the special wards like Shibuya and Shinjuku before covering every single one entirely. The rest of the prefectures of the Kanto region were next with Saitama, Chiba, and Kanagawa being the first to end up under the dilating duo. They were too caught up in their kiss to question how they didn’t explode at this point even as they had now covered the entirety of the Kanto region and were starting to cover the ends of the Chubu and Tohoku regions. Something else they didn’t notice was that they were both starting to drift off,  with Mishima starting to no longer hover over the Tohoku regions.


As they continued to blow into each other, they kept floating and growing over the other regions. Most of Chubu found itself under the shadow of either couple until they stopped floating off and just Mishima covered a lot of the region while Shiho was drifting above the Kansai region. Now it was back to swelling in place as Mishima was starting to loom over the Kanto region and the edges of the Tohoku region once again while his friend had her huge body towering over both Chugoku and Shikoku. 


Eventually they both stopped puff kissing to catch their breaths. Rotating his body around, he saw that he and Shiho covered a lot of Japan. “I’m so big…” he thought. “This is amazing! I’m probably towering over most mountains at this point!” He turned over to face Shiho once more. “Shiho look down below! We’re huge!”


Shiho did what Mishima said and saw that he was right. “You’re right! This is so… breathtaking!” It was impressive that they could hold so much helium and air inside themselves. Yet, Shiho didn’t feel satisfied stopping here. She believed they could get bigger. “You think we could get to the size of the moon?” she asked.


“Don’t see why we shouldn’t try.” Mishima excitedly replied. Shiho smiled before both went in to kiss each other again and continue their growth. Not long after, Shiho started covering up the Kyushu region while Mishima grew to start reaching the rest of the Tohoku region and then, Hokkaido. In only a few moments later, their bodies got large enough to loom over the Sea of Japan and then the nearby countries of Russia, China, and both Koreas. 


It didn’t take long until just one of them completely covered Japan, not that they could take note due to being busy with blowing into each other. The two were lost in each other’s arousal, not noticing how long they were blowing into each other or how big they were getting. However, they had to stop once more and the two did after a while of blowing into each other, not only to catch their breath but to also admire themselves and it was clear to Mishima and Shiho after a few moments of floating about that they both were the size of the moon. Not only that, but their undergarments had snapped off, leaving them nude. Not that they had any shame towards that fact. However, even with their already huge size, they still wanted to get bigger. Without a word, they went back to puff kissing one another. However, their bodies made it clear that they reached their limit as creaking sounds were made from the two and shortly after they were given one hell of an interruption.


*POP*

*BANG*


Mishima and Shiho both exploded as their deflated bodies floated back down onto Shujin’s rooftops. Upon landing, the two laid around dazed and satisfied as their scraps surrounded Shujin. A few moments later, they could hear the voices of Ann and Ryuji calling out. Lo and behold they entered the rooftop with a bewildered look on their faces, both looking to give the pair a talk with the stunt they did.


“Dude, what the eff were you thinking!?” Ryuji questioned almost immediately. 


“Seriously, you two could’ve died!” Ann followed up with, her tone had a bit of worry in there.
“But we didn’t…” Mishima mumbled with as much of a smug tone as he could muster.


“Yeah yeah, we’re into this…” Shiho muttered.


“Well let’s get you out of here, we don’t want anyone to find out who those balloons were.” Ann grumbled, before she and Ryuji tensed up at another voice calling out.


“Ah! Mishima, Shiho! I didn’t think you two were the kind to be into such things!” called out another voice which revealed to be Haru.


“Much less be the kind to do this out in the open.” Futaba piped in.


“If you want, you could join us next time…” Mishima offered.


Futaba blushed a bit at the unexpected offer. “I-I’ll think about it…”


“I appreciate the offer and I’m sure Ryuji and Ann would as well…” Haru cheerfully replied. “Why, they were rather enjoying a similar experience in Mementos…”


“HARU!” yelled out Ryuji and Ann both blushing red in embarrassment. Such a simple mention made Mishima and Shiho blush as well though it was from the image of Ryuji and Ann inflating together as well as the possibility of the others already going through it.


“Perhaps we can get the rest of the thieves….” Mishima whispered to Shiho excitedly.


Regardless of if they could get the thieves or not, they both looked forward to having another session of ballooning and bursting.