Tags and trigger warnings: Emetophilia, vomiting, motion sickness, mild hurt/comfort, Mugen Infinity train arc.

Summary: Set during the Mugen train arc in which Rengoku finds himself experiencing some motion sickness

Posted to Ao3: Apirl 7th 2022

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The Demon Slayer corps, while a powerful organization, was also a secretive one, working round the clock from the shadows to destroy the demons that so frequently preyed upon humans.

Even though the Demon Slayer Corps primarily did their best to work in the shadows their members were allowed special privileges, especially while on duty.

This is exactly why Rengoku, the Flame Hashira, was currently on the Mugen train following multiple credible leads that had spoken of the train becoming some sort of man-eating beast.

Cracking his eyes open slightly Rengoku looks over to the nearby window only seeing darkness and vast expanses of farmland and fields.

"Is something wrong Mr. Rengoku," Tanjiro asked as he looked at the man, a slight scowl on his face.

He, Zenitsu, and Inosuke had boarded the Mugen train with orders to help Rengoku track down whatever demon was causing trouble on the Mugen train, with the crow informing the three boys that casualties involving this train were on the rise.

While Tanjiro had mostly been quiet the other two boys were anything but, with Inosuke, in particular, being in a constant state of awe and excitement over the train itself, frequently banging on the windows and yelling all while Zenitsu tried his best to restrain and calm the boy.

The sight has Rengoku's smile growing a bit. "No, I was merely looking at the scenery. It's been a short while since I've been on a train and for a mission no less," he told Tanjiro as he shifted in his seat slightly.

It felt a bit warm in the train cabin to Rengoku, but considering it was a rather humid night as usual and there weren't too many windows open on the train right now it makes sense.

Although there's something else that draws Rengoku's attention as well, he feels strangely off. There's a strange slight fullness to his stomach at the moment which honestly isn't surprising considering his appetite after all.

Rengoku had a very big appetite to put it lightly, often burning through bowl after bowl of his favorite foods rather quickly. In fact, when the three boys had arrived he'd been over halfway through eating an enormous stack of boxed lunches he'd received as a gift.

All of them were truly delicious, clearly made with love and care so Rengoku honestly couldn't help but indulge a bit.

Now, however, he can't help but wonder if he may have eaten a bit too fast if the strange sensation of fullness in his stomach was anything to go by.

It wasn't painful or annoying but it was a noticeable change in his condition.

Still, as long as it didn't interfere with his demon-slaying abilities he'd be fine truthfully.

He glances down at the medium-sized wooden box on the floor in front of Tanjiro. It was the box that Tanjiro often wore on his back to carry his demon of a sister and protect her from the sunlight that would reduce her to ash.

Since the leader of the demon slayer corps and Rengoku's master had given his approval of Nezuko to Tanjiro, Rengoku kept any unsavory thoughts he may have had on the matter to himself.

A slight scowl crosses Rengoku's face when his stomach makes a soft growling noise and he brings a hand to his stomach almost absentmindedly.

Tanjiro looks at him with a soft chuckle. "Still hungry?"

Rengoku nodded as crossed his arms and closed his eyes. "It would seem so," he murmured. Strangely enough, however, despite his words, he wasn't hungry at all at the moment. His appetite just wasn't there.

Perhaps that should've been Rengoku's first sign that something was wrong truthfully.

~~~

As time slowly passes in the train car the slight feeling of strange fullness in Rengoku's stomach seems to grow strong, settling into a slight queasiness in the pit of his stomach.

It's even warmer now as well, enough that it is becoming just a tad uncomfortable. Rengoku opens his eyes slightly, shifting a bit to get more comfortable.

The floor feels like it's moving ever so slightly beneath his feet despite him sitting still in his seat.

"Mr. Rengoku? Are you alright," Tanjiro asked, sounding slightly hesitant.

"Of course I am! Why do you ask," Rengoku asked, his usual boisterous tone coming out.

Tanjiro chuckles softly, almost nervously. "Well, it's just that you seemed a bit pale." Rengoku's face was slightly pale under the warm light of the train car and with Tanjiro sitting this close he can see the very fine layer of sweat on the man's forehead. Tanjiro couldn't help but be a bit concerned truthfully.

"I assure you I am fine," Rengoku told him, to which Tanjiro merely nodded before turning his attention back to the window beside him.

Rengoku scowls slightly as he places a hand on his stomach, that slight queasiness there is slowly yet gradually growing into something a bit more tangible and his scowl becomes a frown when he feels the organ gurgling softly under his hand. The feeling is not completely unpleasant, but definitely strange and a bit worrying.

Rengoku gently begins rubbing at his stomach as he closes his eyes once more and takes deep breaths in and out. He was fine, he felt a bit full, well a lot full but it wasn't any surprise to him considering how much he'd eaten.

Rengoku opens his eyes slightly only to close them once more, swallowing thickly when the world seems to swim before his eyes, and for a brief moment that slight queasiness sharply intensifies into nausea.

His stomach sloshes, a low gurgling noise coming from it as a wave of nausea rolls over him causing heat to prickle at his skin.

He feels as if he's melting, being exposed to his own flames. All the food he'd eaten sloshing violently in motion with the train as his stomach began to churn rather violently.

Closing his eyes only makes the dizzying nausea all the more worse, however, as he can feel the world moving around him while he sits stationary in place.

Tanjiro looks over at Rengoku when he hears him give what sounds like a soft, almost inaudible groan of discomfort.

Rengoku has his eyes squeezed shut, his face is incredibly pale and coated in a fine layer of sweat. His lips pressed into a thin line as he took deep shuddering breaths in through his nose. Due to being this close Tanjiro can also see Rengoku's throat shifting, bobbing quickly as he swallowed almost frantically.

Something was clearly wrong with him at least from what Tanjiro could see. Tanjiro glances over to where Zenitsu is still trying to keep Inosuke under control inside the train before looking back at Rengoku.

"Mr. Rengoku, are you alright? You don't look too good," Tanjiro asked as he shifted slightly to peer into Rengoku's face.

Rengoku opens his mouth slightly to say something but instantly closes his mouth when the train suddenly seems to change speed, going faster than before and the sudden change in speed has his stomach sloshing violently, his meal from early feeling as though it's brushing against the walls of his stomach.

Rengoku waits a moment or two before trying to speak, muffling a soft nauseated hiccup into his hand when his stomach lurches. "I...I...feel...sick," he mumbles softly in between his labored breathing, the words coming out slurred with nausea.

Rengoku feels incredibly lightheaded, dizzying nausea rolling over him in relentless waves his stomach contents feels all too much like a pot of boiling as it bubbled and churned inside of him. A soft almost airy hiccup leaves Rengoku's mouth when his stomach seems to flip inside of him and he feels bile burning at the back of his throat.

"Huh," Tanjiro said, his eyes going wide at Rengoku's words. Then he begins glancing around, his eyes roving over the nearby passengers. Could it be some kind of demon art-making Rengoku sick all of a sudden considering he seemed fine moments ago?

"Make...it stop," Rengoku suddenly whispers, his breathing labored and his words slurring with nausea.

"Make what stop," Tanjiro asked, concern on his face as he leaned closer to look at Rengoku's face.

Rengoku's stomach makes a rather loud, sickly sounding gurgling noise and Tanjiro sees what little color is left in Rengoku's face seemingly drain away. Rengoku swallows thickly in some effort to clear all of the saliva suddenly overflowing his mouth.

He feels incredibly dizzy and lightheaded, waves of intense nausea crashing over him relentlessly. His body is trembling and he feels weak as if all his energy had been drained in an instant. He groans again, leaning forward and resting his head in his hands when the contents of his stomach seem to roll inside of him with the motion.

"T-The train...it's moving...make it stop...it's making me feel sick..." Rengoku explained his words coming out in a rush.

For a few moments, Tanjiro is quiet simply watching Rengoku then he speaks. "Mr. Rengoku...do you get motion sickness," he asked slowly. While Tanjiro had never been on a train he was familiar with motion sickness considering that one of his younger siblings suffered from it whenever he was riding on one of the horse-drawn wagons.

The thing about motion sickness was it didn't wear off until the person left whatever vehicle or thing causing it.

"I..." Rengoku begins then stops swallowing almost convulsively when his stomach lurches, heaving slightly, and a small splash of bile coats his tongue in the sour, almost rancid taste of half-digested beef and rice. "N-not normally," he manages to chuckle weakly.

One of his hands leaves his face going instead to his gurgling, churning stomach. When he does place a hand on it, he can't help but notice it's bloated slightly, his fingers sinking a bit into the now soft skin there. He can feel his stomach churning like a whirlpool as it gurgles and ripples sickeningly beneath his fingers, clearly upset.

He tries his best to clear the saliva building up in his mouth but with each swallow, it feels as if his throat is slightly clinging together, and the sensation of fullness in his stomach just gets worse simply adding to the dizzying nausea gripping him in its talons.

So he lets it overflow, dripping from his lips almost lazily as it trickles onto his hand and clothes.

"Maybe we should step outside Mr. Rengoku the cold air may help a bit," Tanjiro suggested rather frantically when he sees what little color Rengoku had, had left in his face drain out, leaving it tinged slightly with a green hue that made Tanjiro more than a little worried.

Rengoku opened his mouth to speak but quickly closed it when a loud wet, rumbling burp pressed past his lips. He swallowed thickly feeling bile bubbling at the back of his throat when the burp threatens to bring more with it. Rengoku covers his mouth with his hand as he takes deep shuddering breaths in through his nose.

"I'm going to be sick," he mumbled softly when even more saliva began to flood his mouth, taking on a strange almost salty metallic taste. A sure sign that Rengoku was running out of time to somehow get his unruly stomach under control before he threw up everywhere.

Rengoku's words have Tanjiro moving quickly, practically jumping to his feet and grabbing the man's free hand tugging him to his feet.

Zenitsu looks away from Inosuke when Tanjiro hurriedly walks past them, practically dragging a very nauseated-looking Rengoku behind him by the hand.

"Huh? What's wrong," Zenitsu asked with a scowl.

"Mr. Rengoku is feeling sick. Watch Nezuko for me please," Tanjiro explained quickly as he walked past, not even stopping to look at Zenitsu.

"We're almost there," Tanjiro reassured Rengoku as they entered the next train car which was empty.

Rengoku merely gives a weak groan, another loud burp forcing itself from his lips as his stomach lurches and hitches slightly as if trying to squeeze its contents out.

His legs tremble beneath him like a newborn deer making him nearly stumble over them as the floor seemed to shift and sway under his feet like a living thing, it takes his stomach with it as the organ makes a low, sickly growling noise, boiling and sloshing like a cauldron threatening to boil over.

They're almost towards the door of the train car that would lead them outside when Rengoku suddenly stops walking, instead falling to his knees with a groan of pure misery. His stomach lurching and rolling, the food he'd stuffed inside of it making it ache.

He didn't know why but he felt full, way, way too full and another wet rumbling burp leaves his lips as he all but curls into himself. He's dizzy and lightheaded enough to be almost completely disoriented.

His shoulders shake with a barely repressed heave and he feels Tanjiro tugging on his hand urging him to move but he just can't, at least not with the nausea assaulting him and floor shifting beneath his feet like it is.

Rengoku does not have the strength to stop himself when he gags harshly into his hand, he shakily removed it from his mouth as he places his hand down on the floor to steady himself. He opens his mouth, his breathing labored as he allows the drool overflowing his mouth to trickle almost lazily onto the floor.

He just can't take it anymore and neither can his stomach, he would just need to apologize to the train staff afterwards.

"Oh no," Tanjiro murmured as he released Rengoku's other hand. "Mr. Rengoku are you sure you can't make it?"

Rengoku groans, shaking his head quickly, his throat working as he swallows convulsively, his entire body trembling as his stomach makes low sickly growling noises as it hitches.

Rengoku's breathing begins to stutter, his swallowing becoming audible and Tanjiro sighed softly as he laid a gentle hand on Rengoku's back. "It's probably best if you try to get it up," he murmured as he ran his hand along Rengoku's back.

Tanjiro can't help but remember a moment when he'd done the same for his sibling.

Rengoku groans low in his throat a second before his body lurches forward, a violent, wet retch tearing from his lips bringing a small splatter of brown-tinged bile with it.

It splatters across the floor in front of Rengoku. He pants heavily, his eyes growing wide as he gets the brief moment to breathe before a harsh, wet guttural burp has a large wave of thick brown and tan vomit gurgling up his throat.

It splatters the floor in front of him, the undigested remnants of rice and beef he's eaten forming an almost smoothie-like slurry as it spills from his lips almost lazily.

Tanjiro can't help but grimace slightly, still rubbing Rengoku's back as he glances away. "There you are. Just do your best."

Rengoku gasps for air coughing wetly as he attempts to briefly gasp for air, a river of drool drips from his lips and tongue onto the floor, his eyes glassy with unshed tears from the exertion. His throat spasming slightly with weak gags.

His stomach makes an almost vicious growling noise that makes Tanjiro flinch in sympathy, it almost sounds as if his stomach is snarling and Rengoku groans, clutching at it as he curls in on himself slightly, it felt like a firework had gone off in his stomach.

Rengoku believes at first that he's done but truthfully he should know better considering how many of those boxed lunches he'd eaten. He feels his stomach violently heave beneath his own hand, practically convulsing as it spasms, and a large surge of vomit suddenly rushes up his throat.

It fills his cheeks for a brief moment before pouring from his lips, a loud, rumbling almost guttural retch leaves Rengoku's mouth the noise becoming garbled and wet on the tail end as an enormous wave of brown, thick lumpy slightly vomit pours from his lips.

It adds to the rather large glistening slurry already in front of him, and Rengoku can't help the gag he gives when he notices he can easily make out the beef and rice among the mess.

This was all rather humiliating as well, it may not have been an issue normally but considering he's already making a mess of the train car, while Tanjiro is helping him and watching him well it definitely had a slight blush burning Rengoku's cheeks.

"Hopefully it eases up once you get everything up," Tanjiro chuckled sheepishly.

Rengoku says nothing merely giving a miserable, weak, slurred groan in response as threads of drool and bile drip from his lips. He swallows thickly as a wave of overwhelming nausea engulfs him, the almost rancid sour scent of vomit filling his nose.

That, along with the utterly horrific taste coating his mouth and the fact that he is looking at the undigested pile of his dinner sitting in front of him, only has Rengoku retching again.

His body lurching forward as he gave a wet, sick-sounding, gurgling burp as his upset stomach heaving again and sending up another thick, large wave of vomit, adding even more of his undigested dinner to the growing slurry on the floor.

Tanjiro can't help but be morbidly fascinated by how Rengoku is bringing up, his eyes glancing down at the enormous pile of vomit at their feet after all he's never really known a person that could easily eat nearly 20 or so boxed lunches on their own.

He can feel Rengoku's spine curve and his body shudder with each heave and gag, the muscles in his back tensing and he has a feeling that Rengoku will be feeling rather sour and exhausted once everything was said and done.

Rengoku gives one last guttural retch, his body lurching forward as an enormous wave of vomit surged from his mouth, it pours from his lips almost lazily for a few moments giving him no chance to breathe at all.

Eventually, though it tapers off leaving Rengoku panting and gasping for air, bile and drool dripping from his lips in thin threads.

"Careful," Tanjiro murmured, grabbing Rengoku's shoulder when he sat back with a sigh.

Rengoku has his eyes closed, a scowl tugging at his lips as he rubs at his stomach with one hand, a series of hiccups bubbling out of him that he doesn't bother muffling. He can his stomach hitching a bit beneath his hand still unsettled, as the back of his throat spasms ever so slightly with weak gags, his gag reflex still incredibly sensitive. He wipes his mouth with the back of his hand as he sniffles softly staring at nothing in particular.

Although now he feels, far, far more aware than he did before the almost violent nausea quickly receding and dying down, settling into a faint twinge of queasiness in the pit of his stomach.

The floor no longer feels as if it's writhing beneath his feet and the overwhelming dizziness he'd felt moments ago is beginning to disappear.

His throat feels raw as if rubbed with sandpaper, and his stomach is sore as well as being still a bit unsettled but, it's a far cry from the motion sickness hell he was in moments ago so it's fine in Rengoku's book at least.