"Are you sure you really want to do this?"
Gumball was still highly skeptical of what the man lying down in front of him had asked him to do. Sure, he was offering fifty bucks for basically nothing, but the young cat still couldn't wrap his head around the request.
The man lying on the ground was essentially a stranger to him. He seemed friendly and approachable and was even charismatic when asking Gumball to sit on his face. He had asked with such confidence and charm that Gumball wasn't sure he heard correctly at first. But after further interrogation (and raising the originally offered $25 to an even fifty), Gumball was sure that the man had thought it through.
He wanted Gumball to lay his plump ass on his face.
"Well... here's go nothing, " Gumball thought to himself, placing his feet on either side of the man's body. He started to lower his butt when the man abruptly spoke up.
"Pants off."
Gumball stopped in his tracks and stepped away. That wasn't part of the deal, and it's not like he was gay! He was just doing it for the money. But fifty dollars didn't cut it anymore, not if the creep wanted Gumball to be in his undies!
Sensing Gumball's shock and reluctance, the man smiled. 
"I'll give you a hundred."
A hundred bucks?? To the twelve-year-old, it seemed like that amount of money could buy him anything he wanted! But his excitement about the money came crashing down when the man continued.
"But your underwear needs to come off too."
Gumball was just about ready to walk away at that point. Sitting on the man's face was weird enough, but naked? That was just gross.
Still... a hundred dollars was a hundred dollars. And the guy was fully clothed, so how gay could it really be? Besides, the pedo creep deserved to suffocate anyways. But despite his confabulation, Gumball still couldn't bring himself to pull down his pants, much less his underwear.
"N-no way man, that's like, super gay!" 
"Two hundred."
The man didn't even hesitate to say it, but to the boy whose main source of income was the $10 weekly allowance he got from his mom, $200 sounded like he could buy a mansion! The man was staring at Gumball, who was standing still, weighing out his options.
"He just wanted me to do it for ten minutes, " he thought, "besides, two hundred bucks? I could buy The Tale of Zelmore III with that kind of money!" He gulped, and slowly started pulling down his beige pants.

They normally took some effort to put on and take off, the boy's bubbly butt proved too large for the tight jeans to easily slide over. But he was soon able to pull them below his ass, exposing his white underwear, straining to contain his massive backside. 
The man simply laid there smiling, enjoying the show. He was happy he had stumbled upon this boy; his ass was exceptional.
While pulling his pants all the way down, the man started at Gumball's small bulge in front of his underwear jiggling up and down. Gumball was small, but the boy didn't know that, or particularly care. Sure, he had rubbed his crotch on his mattress once in a while, but other than that the boy wasn't interested in sex. Even while hanging out with his girlfriend, the boy was innocent.
His pants were finally fully off, and he took a deep breath. "Two hundred bucks" he whispered to himself. He closed his eyes and cringed as he quickly pulled down his underwear. His tiny blue dick and balls swung free, his ass bounced and jiggled from the quick motion. 
He turned away, finally exposing his naked ass to the man. It was so plump and smooth, tiny droplets of sweat covering the bubbly mounds. 
"Spread them”
He was grossed out by the request, but it's not like he didn't see it coming. And he had already come this far, does it really matter if the man sees his asshole too?
The boy's fingers plunged into the pillowy cheeks and he pulled them apart. The boy's cute butthole was bright pink in startling contrast to his blue fur. It was twitching slightly, evidently not used to being exposed to the cool air as it was normally covered by the twelve-year old's pert rear. 
"Now sit."
With one big deep breathe, Gumball lowered his ass onto the man's face. He cringed as his sweaty, hot but made contact with the man's cold face. His asshole was right on top of the man's nose, a feeling that made Gumball shutter. It's not like it felt good (that would be gay!), but Gumball couldn't ignore how strange it felt to have his asshole rubbing against the nose. 
Once he was fully sat, Gumball let go of his cheeks, and they clapped back together, fully surrounding the guy's face. 
"Just ten minutes..."
The man breathed in deeply through his nose, basking in the sweaty, earthy scent of the cute boy's asshole. His fat dick pulsed and throbbed in his pants, straining against his jeans.
Gumball couldn't help but notice the man's bulge. It was huge! At least six inches. The boy looked away, trying to focus on anything but the fact that his dick was started to throb, and although the man seemed content with Gumball's stationary ass, the boy couldn't help but start rubbing his ass back and forth on the man's nose, the very tip of it slowly easing into the twitchy hole. 
"Why does this feel so..." Gumball kept rubbing his ass. He wasn't happy with just the man's nose, he needed something better, warmer, and... longer. "So... good.'
He slid his ass down the man's face, placing his asshole right on top of his mouth. "L-l-lick it." Gumball was feeling more confident, and his fully erect dick reflected that. If the creep was gonna make him do this, the least he could do is enjoy it.
His tongue slowly slid out of his mouth, licking around the boy's asshole, all the way down to his chubby taint. The man brought his hands to Gumball's ass, squeezing the bubble butt, feeling his fingers plunge into the sweaty flesh. 
Gumball's dick started cutely dripping precum onto the man's chest as the tongue slowly eased its way into the warm depths of Gumball's asshole. His corkscrewed his way into the hole, loving how slick and hot it was. The boy moaned as he pushed it in ever deeper, giving the hole kisses as his tongue pressed against the boy's virgin prostate.
"Ugh, this is so nasty!" The boy moaned, his dick now constantly leaking precum. He had never felt so good in his life. The tongue twirled deep into his asshole, as he shook his ass around the man's mouth, making him feel the heaviness of each jiggling cheek. 
The man's licking got sloppier and wetter, his tongue helplessly licking all of Gumball's most intimate parts. It flicked against the boy's balls and taint and explored the sweaty depths of the cat boy's inner cheek. In response, Gumball started sliding his ass all around the man's face, using it like a soaking wet slip and slide. His dick bounced around, throbbing and leaking over the guy's face and chest and Gumball pulled the man's hair and forced his face as deep as it can go. "Stick your tongue in! All the way"
The man did just that, drilling his wet tongue deep into the tight hole. And with that, the building pleasure in Gumball's body exploded through his cock, spewing milky white kiddie cum over the stranger's chest, moaning and groaning as pleasure racked the boy's body. His legs shook as the guy's tongue pressed hard against his prostate, forcing more and more cum out of the kid's cock.
After fifteen seconds of sloppy, saliva-covered milking, Gumball finally slid his ass off the man's face, his whole body collapsing onto him. 
After taking a minute to regain his senses, Gumball stood up on wobbly legs and walked towards where he had left his clothes. He was embarrassed at how into it he had gotten, and dressed himself as quickly as possible, desperate to get home and forget this ever happened. As he started to walk away, the man stopped him.
"Hey kid, here's your money."
In his enthralling pleasure, Gumball had forgotten all about his payment, and ecstatically grabbed the two hundred dollar bills out of the stranger's hand.
Maybe he would try this again some time.