[Assnosis, Ass Worship, Yaoi]

The Holy Grail War. Wars that all revolved around a single wish that seven people wanted to fight over. A wish that would belong to the one that managed to command their Servant to grasp victory. That's what the Holy Grail War boiled down to. A fight for something that shouldn't be possible to attain.

But not every participant in those wars was on the same level. And sometimes, a complete ignorant individual managed to worm his way into the competition. It had happened in other timelines, where those that shouldn't actually have become maguses managed to get ahold of a Servant, and simultaneously throw everything off the rails. And that would happen once again, as a young man wandered into a warehouse he really shouldn't be in.

"Can't believe I had to run just because I couldn't pay..." The young man, a simple blonde youth by the name of Kouki, sighed as he hid behind one of the walls inside the warehouse. Okay, so he had done a little crime, but he really needed that bread. He had run out of money weeks ago, and his supply had run low. He was going to ration it as much as possible, so he was actually making better use of it than most other customers... Actually, now that he thought about it, didn't that make him worse because he didn't pay for extra food like them?

Kouki slowly rubbed the back of his head as he sighed. Ah, what the hell. It wasn't like he was going to find the proper answer to any of that. He just had to be grateful that he managed to get away. Now, where had he ended up exactly? He just started running and didn't think too much about where he ended up, but... This was definitely not anywhere close to home. This was more like one of those joints that you'd see in crime shows. At least nobody was around.

But there was something that caught his eye. A big glowing circle with some mud in the middle? Weird, why'd somebody go through the trouble of drawing this elaborate figure and then just dump a bunch of crummy mud inside it? Eh, might as well go check the stuff out and see if it was worth anything...

Just as Kouki walked into the circle, he let out a sharp cry as it felt like something had just shocked right through him. Not just that, but he could feel something wet leaving his fingertips. Upon looking at his hand, he had to grimace as a couple of drops of blood had managed to pour forth from a tiny wound. He really didn't know how he had gotten that wound, just that it wasn't very pleasant.

He didn't get to dwell on his pain for too long before that circle started to glow violently. Bright, deep red. Spreading outward as it managed to fill the entire warehouse, with the glow getting so bright that Kouki just had to cover up his eyes so he wouldn't end up going blind. Man, was this some sort of advanced light show that he stumbled on or something?

"Who dares call upon the King of Heroes? Who dares summon me to this time?"

A voice echoed out, a very annoyed and thoroughly disgusted voice. A voice that sounded real handsome, if he had to be honest. But Kouki still kept his eyes closed and his face covered because he was still too vulnerable to the bright light. Did he need glasses or contacts? Had he been sensitive to light all along? Maybe that explained why he didn't like to be around during the day...

"I asked you a question, Mongrel!" The loud voice shouted at the blonde boy, as a force of pure power started to blow right past the boy. A force that made him drop his arms, with none of the light thankfully still remaining in the air. He could actually see things... And people, especially the handsome man in thick golden armor that was standing in front of him.

Kouki had never seen a man as pretty as him. No, he wasn't just pretty... He was something beyond his comprehension. The design of that armor was definitely ancient. He hadn't seen stuff like it in the books that his dad gave him, and he definitely hadn't seen stuff like it on TV. The closest he could think of were those golden egyptian duds, but they were nowhere near as thick. Who... Who was he..?

"Uhm..." The blonde young man muttered as he slowly looked at the equally blonde figure, who just kept growing more and more annoyed at his weak and meager personality. "I-I'm Kouki, I, uh... D-don't know what you mean by summon, and I've not really heard about a King of Heroes..." He had to be honest. Sure, he wasn't exactly above lying here and there to try and get by, but something told him that if he wasn't truthful to this man, then... Well, his head was probably going to roll.

The golden-armored man glared straight at him. This boy... This MONGREL, was his Master? He had no real magic potential! In fact, it was a wonder that he had actually managed to manifest, considering he barely felt any mana pouring from him. Maybe it was the ritual that sustained him. Regardless, he was part of another Holy Grail War. And he had already managed to lose, just from the fact that he had been summoned by...

He paused, as he felt a second faint source of mana. And then he looked down, and saw mud smothering the circle beneath him. That explained everything. This boy had managed to acquire mud that contained the faintest trace of his old friend. How? He did not truly know. But what he did understand was that the boy had done something that should be impossible. Call upon him despite no inherent magical potential. No matter. If he was feeding on the remaining embers of his old friend's Mana, then he could at least last a day.

"Mongrel." The golden-armored man said, as a simple blade slowly started to push out of the air beside him, letting him draw it as if he was drawing it from its proper sheath. "Know that I am the King of Heroes, Gilgamesh. And though you shame me by being my Master and summoning me despite your inadequate nature, I will give you a swift death. You shall suffer, our bond shall be broken, and I shall find somebody that can properly satiate me with the mana I need to keep manifest in this rotten day and age. Now stand still!"

Kouki's eyes widened. He still didn't know who Gilgamesh really was, but he was definitely bad news. He managed to pull a sword out of thin air, after all! That was bad, way bad! What was he going to do to stop it? What could he possibly do to stop it? He wasn't sure, but... M-Maybe if he just... N-No, there's no way that'd work. He was super strong, and it had only really worked on cops or cashiers that weren't ready for it. But... M-Maybe!

Gilgamesh dashed forward with his blade in his hand, as he watched the boy suddenly spin around and drop his pants in a mere instant. The boy was a lot more agile than he look...ed...

Just as Kouki had managed to turn around and drop his pants, it was like a golden gleam started to shine forth from that surprisingly shiny and yet plump posterior. A gleam so bright that the light was reflecting within Gilgamesh's eyes, the King of Heroes honestly not sure how to respond. He had fought plenty of enemies during his life. Plenty that were out for his head, his kingdom, or his friends. But this? This was an enemy that would willingly just debase himself for the sake of his own life...

"What in the world are you doing, Mongrel?" He couldn't muster up proper rage as he addressed the young man. All that he could do was stare straight at that rear, his mind trying to figure out what exactly the boy had thought to achieve by doing this. What would this mongrel... This... This mongrel...

Gilgamesh trembled the more he tried to focus on the boy. Something was messing with his head. Maybe if he looked at that butt a little more, it would... N-No, it had to be the source of this haze inside of his mind. What exactly was it doing to him? And for that matter, why was it so immaculate? He had only seen butts that perfect back in his age. And the only ass that even came close to comparing was Enkidu's, the same ass that had claimed some of his first passionate nights...

Kouki slowly looked over his shoulder as he watched the golden-armored man slowly struggle to fight back against the influence of his posterior. It had actually worked. Well, somewhat. The cops that he mooned like this would usually spring to attention and be nice and obedient within a few seconds. Same with the cashiers. He really was made of strong stuff if he was able to resist this long.

"You like it?" He chimed, almost as if he was teasing the King of Heroes in the process. "I mean, you can come closer if you'd like a better look. I won't stop you." He continued, all while letting his hands sink into that meaty flesh. Squeezing and toying with it, letting his fingers bring more emphasis to it...

Gilgamesh gasped and trembled a bit more as the way he played with that rear was making the finer details pop out. The small freckles that gave it extra character... N-No, he was being deceived. That ass should be vanquished before it did more to his mind than he was able to handle. "Wh-What is with this rear? You do not have any proper control over your potential as a Magus, so why can you toy with my mind like it's made of clay? Answer me, Mongrel! Unless you want that rear carved from your body!"

Kouki felt a bit of sweat run down the side of his head. Even though he was pulled in by his ass, that King was definitely still going to kill him if he tried to let up. "I... W-Well, my Dad always told me that we had a gift. I didn't really pay attention or anything, but he said that we were descendants of some really hot concubine, and she used her assets to control men. He showed how effective it was by getting us off scot free from some debt that he had racked up, and taught me to use that power with responsibility if I ever needed to do so." He explained the best he could, before chuckling a little. "I'm not sure if pulling in a King like you is that responsible, but I don't think it's that bad. I mean, you really like it, don't you?"

Gilgamesh was fuming. The boy may not be a Magus, but he definitely had traits that would've made him an effective one. If he had even bothered to try and tap into his potential, he would've fallen prey to that ass in a matter of seconds. Now that he knew that he wasn't able to control it as effectively as one might expect, he could cut him down...

After he finished admiring it, of course. It was still a rather nice rear. It was a shame that it belonged to such a Mongrel. If it belonged to somebody like Enkidu, he would've started to slobber and worship it in an instant. Of course, only his dear Enkidu would know about his submissive and obsessive side. There was no way that he was going to act that way to some Mongrel from the modern age. He had grown so lax that he didn't even take advantage of the gifts that he had been given...

Kouki could see the internal struggle thanks to Gil's expression being very telling. He was making all his thoughts perfectly clear, to the point where he hadn't even noticed the drool running down his chin. Maybe if he amped it up a bit and started the hypnotic movement that his Dad told him would ruin any man that looked at his ass? How'd it go? Back and forth? No, it was right and left...

Gilgamesh watched carefully as his mind continued to rationalize that looking right at that hypnotic ass was definitely a good thing. Watching it sway left and right. Watching that plump posterior bounce and wobble with every sway. It was so... So engrossing. He just wanted to dive down in between those cheeks and eat him out. He wanted to get a taste of those cheeks...

"You know, Dad told me something." Kouki said, still keeping an eye on the golden-armored man that had been pulled in by his ass. "The longer you look at me, the quicker you fall into a complete and unbreakable trance. It also helps awaken the submissive flame inside a man who claims to be straight, but, like, I've not seen a single straight man actually fall for this ass. All of them turned out to be gay."

It was clear that his explanation was falling on deaf ears. Because Gilgamesh just kept on looking straight at that ass. Watching it sway left and right. To the point where that swaying motion was causing the color in his eyes to flicker back and forth between many different kinds. To say that he was utterly hypnotized and enthralled by that ass was an understatement. He was... Oh, he just wanted it...

"It's okay to love ass, Gil." A soft voice spoke through Gilgamesh's ear. A soft voice that sounded so familiar. Why was it familiar? He couldn't exactly tell. But he knew that he liked how it sounded. He liked what it was implying. He really did love ass, after all. So the fact he wasn't going to be blamed for it any longer... That brought him a lot of joy.

Gilgamesh drooled more openly as he took a single step towards Kouki's pendulum of an ass. "It's okay to love ass..." He muttered in a trance, his expression turning from placid and only mildly emotive to a bright and almost ecstatic smile...

"You know, to love ass means to obey it. Obey the man that owns that ass. You can do it, right, Gil?" The soft voice echoed through his mind once more, and it just sounded right. The idea of giving everything to the man that owned that ass... That heavenly derriere. It was the right call.

"Obey... Obey the man who owns that ass..." Gilgamesh recanted what he was being told. Drooling more openly as he fell onto his hands, crawling towards the rear on all fours. Even though it was degrading, he didn't think it was anything that he should worry about. Not when he had an ass to worship.

Kouki watched the golden-armored man creep towards his ass, and he could feel his cock growing harder by the second. He had seen people fall in love with his ass before, but this was... Oh goodness, it was something else. And he actually really liked it. Like,  he wasn't sure if he could really call himself gay, but if this was what happened when he put his ass to good use, then he might as well go all the way and indulge...

A smile crept onto his face as he started to speak at the same time as the hypnotic voice inside Gil's head. "Strip." A single word that sent the King of Heroes' mind reeling, unable to truly recover as it was like he was about to climax from obeying the commands that he got from his Master.

"Yes, Master! Gil will strip!" The King of Heroes gave in and obeyed the order, as he was very briefly covered in the same kind of golden shine that had pulled him close to that perfect ass. And when the shine vanished, the King of Heroes was completely naked. Every single inch of his well-trained and perfectly maintained form was on display...

Though it was hard to see it due to the angle, Gil had to be hard. How could Kouki tell? Well, he was leaking so much cum onto the floor that he had already made a puddle. He was on the verge of cumming everything out. And all he needed was that final push. The little nudge to make him cum out everything that made him such a powerful King. And that swaying ass that had already told Gil so many sweet nothings would be the one to finish him off.

"Gilgamesh." The voice echoed, and Gil obediently froze. He even trembled a bit as cum started to bubble forth from his cock a little more. All while he waited. "No longer the King of Heroes. But the Slave of Butts. A fitting title for a devout believer like yourself, don't you think?"

Gilgamesh trembled as the new title echoed inside his heart, and engraved itself on his very existence. The King of Heroes was no more. Now only the Slave of Butts remained. Something that he had to admit to the world. "I, Gilgamesh, am nothing more than a Slave to all the Butts in the world! Master, please! Please give me your butt! Please, I want to make sure that it gets all the worship that it deserves!" He cried out, all while that mesmerized look in his eyes grew all the more intense. All those colors spiraling repeatedly as he kept drooling. All while forcing himself to stand back up and present himself like a dog standing up on his hind legs, showing off his painfully erect cock that was audibly and visibly squirting out plenty of cum, the delight of serving his Master causing him to orgasm...

Kouki had to laugh a bit. A laugh that the voice inside Gil's head echoed, with the Slave of Butts none the wiser. He honestly didn't think ill of the fact he was being laughed at. He was just enjoying it. Enjoying the sensation of serving his Master... "Here, Gil. You want it?" He asked, all while backing up ever slightly. Just enough that Gil's face was closer to his ass...

Maybe a little too close. Because as soon as he got close enough, Gil pushed his face right up against that ass. Planting kiss after kiss after kiss. So many kisses that Kouki was the one being overwhelmed this time around. He couldn't really process all the different spikes of pleasure pouring through him. So much was happening at the same time, it was getting... It was..!

This time, it was Kouki's turn to orgasm. He cried out just as he felt Gil's loving lips push right up against his puckered asshole, the sensation spreading through him making him cum. Hard. So much so that his cum shot straight ahead, splattering against one of the many crates that decorated the warehouse. All while he felt his legs slowly giving up. To the point where he was almost going to collapse and fall onto his stomach...

Only for his Slave to grab him and stop him, while still pressing his face right up against that ass. "Master, are you satisfied? Did your Slave of Butts do good? Are you happy with your orgasm, or would you want another?" Gil was so obsessed that he was practically asking for confirmation that he had done a good job. He really wanted to make sure that his Master was satisfied. It was the single thing that he lived for. his Master's absolute entertainment and thorough satisfaction...

Kouki let out a sigh of relief as he used Gil's face as a seat, the former King eagerly licking away at his crack while he tried to catch his breath. He really was something else. Not just with all the power that he had at his disposal, but how much he changed once he had seen things as he really should. It was...

A single idea started to bubble into his mind. Hold on. He said he would look for somebody else to serve, so he could stay around more. If that was the case, then there were more people just like him, right? And if that was the case, then there had to be some sort of prize on the line. What if he ended up winning and he got that? If so, then he could... Well, he could do whatever with the prize. Whatever it was!

With that, new energy filled Kouki. He got up onto his feet, his Slave getting a nice view of the ass-shaped Command Spell that was emblazoned on his nuts, while he looked over his shoulder and looked down at Gil. "Slave! We have a big fight to win! I trust you'll do everything in your power to make it happen!"

"Gladly, Master! Anything to make you and your heavenly ass satisfied!"

---

Kouki was expecting things to go smoothly. He didn't expect the city to be practically leveled in the span of an hour and for him to currently be sitting on top of Gil once more, now looking up at a big cup floating down from the sky. Then again, what could he have been expecting?

Gil went all out. He used everything at his disposal and completely annihilated the opposition. All while promising his Master that all the damage that he caused could be undone. Sure, people would probably get a flash of his ass once they were being reconstructed, but that was a blessing as far as he was concerned. All he had to do was make a wish on the Holy Grail...

"So this is it?" Kouki asked, as he felt his Slave nodding and rubbing his face up against his cheeks. "I just have to wish on this thing, and everything I ever want'll come true?" More nodding, with Kouki trembling ever slightly as he managed to rub a really itchy spot on his ass. He'd have to ask him to massage his crack with his tongue when they were done here...

What could he wish for, exactly? There were a lot of options. And not all of them were exactly equal. Sure, he could wish for a lot of money... Or he could wish for a lot of boys like Gil... Or he could wish for eternal life. Hmmm... Wait, he could wish for more than one thing if it was in the same wish, couldn't he? There weren't any rules as far as he was aware...

"I wish for Money, Life and my Powers at their Peak!" Kouki cried out, closing his eyes almost instantly afterward as a bright golden glow poured out from that big ol' cup that hung in the sky. Goodness, it was so bright that he almost couldn't see. But he could definitely feel something welling through him after he had uttered his wish. Something powerful. Something that made it seem like he truly had gotten what he wanted.

But he's not the only one that deserved a wish. As he slowly lifted himself off his Slave's face, he looked over his shoulder. "Slave. What do you wish for?" The Holy Grail seemed to have enough power left in it for a single wish. And since his Slave had done such a good job and made him so happy with how he had destroyed the competition, it only made sense to give him the chance to get his own wish.

Gil panted a little as he looked up at the Holy Grail. A cup that he truly did not care for. He was more into seeing how the world had come and gone since he departed from this life. At least, that was his original goal when he was summoned. But now that he had become a Slave of Butts, a Slave to his dear Master specifically, there was a brand new goal in mind.

He seized up for a moment as he tried to speak. Something was holding him back. Something was preventing him from uttering those fated words. What was trying to make him act against his true nature? Whatever it was, he didn't like it. He didn't want to act like he wasn't a Slave of Butts. That was his true nature! His only reason to exist!

And to deal with this problem, he cast his gaze towards his Master's heavenly ass. And it all just washed away. Such a delightful feeling rushing through him. A feeling of pure bliss... It was wonderful. So wonderful that it made him cum right then and there, as the fateful words left his lips and allowed him to proclaim his wish.

"I WISH TO BE A SLAVE OF BUTTS FOREVER! EVEN IF I RETURN TO THE THRONE, LET ME REMAIN A SLAVE TO THESE WONDERFUL BUTTS THAT HAVE SHOWN ME THE PATH!" He shouted from the depths of his engraved soul, cumming violently as he finally tossed his Kingly title away. He didn't need to be a King. He just needed to be a complete and utter slave. Nothing else...

The Holy Grail responded to his wish by glowing... and then disappearing. All while a mark not unlike the one that had appeared on his Master's balls appeared right over his butt. The sign that denoted him as an eternal slave. Specifically towards asses as perfect as his Master's. Other butts were good too, but he would betray any other ass for the sake of being with his Master's. He'd follow him in any world... But he would keep himself occupied as long as he wasn't aware of his existence...

Kouki giggled a little. All while taking his seat on top of Gil's face once more. "Thanks, Slave. Breathe in as much as you'd like, I'm sure you'd like to cum a lot if that's the kind of wish that's hidden in your heart." He chimed, and he immediately heard the frantic snorting echoing from his Slave's nostrils...

He was satisfied. And he couldn't help but wonder, would the wish truly reach those other worlds..? ...Were there other worlds, for that matter? Ah well, it wasn't something that he had to worry about.

Not while Gil was going to worship him until the end of time itself...

---

"G-Gilgamesh, what is the meaning of this?!"

"Master, please! Place your rear on my face! Use me as your seat!"

Tohsaka Tokiomi had difficulty trying to court Gilgamesh's favor after summoning him. He was a very difficult Servant to work with. So imagine his surprise when he was suddenly confronted with this sight, right after he had to reprimand him and try to argue for their victory to be more decisive...

He was not a crude man by any means. But seeing Gilgamesh kneeling in front of him, begging to be sat on... There was something about it that he just couldn't ignore. "V-Very well. But in exchange, we wipe the enemy from this city as soon as you're done indulging your dirty urges." He muttered, all while giving the King of Heroes exactly what he wanted...

Gilgamesh let out a delightful moan as his Master sat on him, cumming inside his armor. "Yes, Master..!" The Slave of Butts would do anything, as long as his basic need was fulfilled. Ah, he had been suffering from ass withdrawal for so long...

If he could keep enjoying an ass like this, then breaking out Ea wouldn't be an issue...

---

"A faker's ass... Mmmph, it's perfect. In trying to replicate my weapons, you've achieved something so much greater..."

Emiya Shirou was beyond confused. One moment, he was locking blades inside of Unlimited Blade Works. And now that King of Heroes that had caused everything to go south had pulled his pants down and started to make love to his rear. Honestly, he didn't know what to truly say in regards to this development, but...

If he could buy a bit more time for Saber to finish destroying the Grail, then letting Gilgamesh eat his ass out wasn't that bad. Besides, it was starting to feel a little good. Maybe he should lean in and use him as a seat...

Gilgamesh cried out as he felt the Faker's ass squeeze onto his face, trembling as his inner Slave awoke. Yes, this was the ass meant for him. An ass that would satisfy him, even after he had incarnated into this world.

Now, to give it all the love it deserved...

---

"S-Senpai? W-What's going on?"

"A-Aha... To tell you the truth, Mash, I have absolutely no idea."

Fujimaru Ritsuka really wasn't sure how he could possibly explain what had happened. He managed to summon the King of Heroes. Two of him, even. The younger Hero, and the older King. The Archer and the Caster. And what happened the moment they got their eyes on him?

He ended up with them on their knees, both of them pressing their faces up against his ass cheeks. So much so that the only way that he could satisfy them was by taking off his pants and just letting them indulge, something that caused the sweat to pour down the side of his head.

"Can... Can they still help us like this?" Mash Kyrielight, the boy's personal partner and Shielder Demi-Servant, didn't know how to react either. She just tried to keep focus on the mission at hand. Could these two truly help them fix Human History if they were like this?

Ritsuka didn't know the answer. And to be honest, if they kept kissing his ass like this, he wasn't sure if he was going to care too much. If they just kept worshiping him, then...

"Actually, Mash... Could we try and summon more of them..?" A leery smile worked its way onto the black-haired boy's face, as a new dominant side started to form within him.

---

Across all worlds, events like these became more and more common. All of the different Gilgameshes begging to be useful to the first male ass they saw. Begging to indulge and worship. Truly a Slave of Butts, as he wished for himself to be.

All while the original, the one that had made the wish in the first place, became little more than one among many slaves to his Master's butt. But did he mind? Of course not.

He still served his Master. As long as he was happy, then the Slave of Butts was happy. And he would remain happy, until his Master finally decided that he didn't need him any longer...