Disclaimer: I do not own Saiyuki. I do not have the capacity of mind to have created Saiyuki. But I am going to do unspeakable things to the characters. Bwhahahahahaha!

Author's Note: I don't think I'm that great at writing, but I don't think anyone else is going to do what the ideas in my head are. Also, for those of you who watch the anime, Hakkai will have a glass eye like in the manga rather than a slightly deformed eye like in the anime.

Partial Differentials

Chapter One: First Order Derivation

Son Goku couldn't sleep. Okay, that is an incorrect statement. Son Goku could sleep through the apocalypse and still wake up after it was all over yelling, "Harehetta!" at the top of his lungs to all of the charred and mutilated bodies. He could sleep as a hundred or more youkai descended upon him to decimate his body and tear him limb from limb and still wake up the next morning saying, "Harehetta!" again to dead and mutilated bodies, but this time, he would have been the cause of death and mutilation, not the apocalypse. In fact, in any situation a person could possibly fathom as not being sleep through-able, the end result would be the same, with Son Goku remaining firmly asleep and still waking up in the morning saying, "Harehetta!" only not necessarily to dead and mutilated bodies.

Most of the time, the bodies on the receiving end of Goku's most frequent statement were very much alive and, depending on which person, not too thrilled to hear it for the umpteenth time.

Body one belonged to Sha Gojyo, a hanyou with long hair and striking eyes, both the color of blood. If he were the first to respond, he would lazily reprimand the youth with a "baka saru" thrown in for good measure. This would cause said saru to respond with insults along the lines of "ero kappa" and such. The two would then exchange many similar insults back and forth with escalating volume until another, very irritated, voice would drown out both kappa and saru while dealing each a blow with a paper fan. Sometimes, the fan would be bypassed in favor of a few very close, but not fatal, shots from a Smith & Wesson, five round exorcism gun.

The person carrying that gun was body number two, which belonged to Genjo Sanzo, a high Buddhist priest who didn't believe in Buddhism. This man had skin so white, it made one wonder whether he had not been living in a basement his entire life. His hair was gold (Goku thought it was bright as the sun), and his droopy eyes were a deep shade of violet. It was an interesting combination, and along with his face, people sometimes thought that Sanzo was actually a woman, much to his chagrin. He became irritated easily and often, most of the time because of said saru and kappa, and was not adverse to using violence and death threats to get his way. Once he did however, it was not long before something irritated him again.

Usually when this occurred, "Maa, maa…." would come the voice of body number three, the third and final body of the rest of this ragtag bunch. This belonged to Cho Hakkai, a human turned youkai who had short black hair, one green eye, and one glass green eye hidden behind his bangs and a monocle. He had formerly ripped this eye out in his dark and murky past for reasons which will be explained later, although anyone who reads this probably already knows them. Anyway, Hakkai was the most polite and reserved member of the group, and he was not as irked by Goku's and Gojyo's antics as Sanzo was. In fact, it usually seemed as if he enjoyed the two's constant irritation of Sanzo more than anything else.

So it was, with this group of four who traveled west, a daily routine punctuated by fights with crazed youkai and ending either at an inn or camped out somewhere in the wilderness. This particular night found the group at a small inn in a small town, resting up for what the next day would bring. They had participated in a small skirmish earlier that day in the woods surrounding the town with a small and relatively harmless group of youkai. No one in the ikkou was hurt. In fact, none of them had put any serious effort into the fight to begin with and it was over with relatively quickly.

When they had reached town, they partook in dinner as usual, with Goku and Gojyo fighting over food while Sanzo grew murderous and Hakkai grew amused. Afterwards they had paired off for their rooms as usual, Sanzo with Hakkai and Gojyo with Goku, and were currently in the process of getting a good night's sleep. All, that is, except for Goku who was currently tossing and turning restlessly, much unlike his usual self who slept like the dead while snoring loudly like a lawnmower.

This did not go unnoticed by his current roommate. Gojyo normally did not have any problems getting to sleep when Goku was partaking in his regular sleeping pattern. The snoring, while loud, had become to Gojyo a white noise which he could now drift off to without a second thought. Right now, however, the room was entirely too quiet, its silence broken frequently and irregularly by Goku's constant shifting. This break in the normal pattern was clearly noted by Gojyo who was finding it that much harder to drift off. For a while, he thought that this irregularity would soon take care of itself and the saru's snores would start drifting his way. When an hour had passed, however, the kappa became too irritated and decided to get down to the bottom of the whole situation.

"Oi, saru, what gives? I'm trying to sleep here."

"I'm not making any noise, kappa, and stop calling me saru."

"That's the point, saru. You aren't making any noise. So, what gives?"

"Nothing, kappa, so go to sleep and leave me alone."

Gojyo could tell something was definitely wrong given the slight desperation he had just heard in Goku's responses, and he was slightly miffed that he had been so readily thrown off in his show of concern. For concern it was, much as he would ever hate to say it out loud, that kept him from simply ignoring the boy and trying to sleep as usual.

"Look, baka, I can't sleep with you rustling over there, so tell me what's bugging ya so we can both get back to sleep."

Goku paused for a moment before he responded. He knew Gojyo was worried about him – after two years of traveling together, he had finally picked up on the man's protectiveness and concern for him – but what was keeping him awake was far too embarrassing for him to just tell Gojyo outright. He would surely die of shame.

Noting the pause, Gojyo sat up and look across at the younger man noticing the slight frown and…was that a blush on his cheeks? Now he definitely had to find out what was eating the saru.

"What is it?" he teased, "Thinking about that girl who came on to you yesterday? Did she make you 'excited'?"

"NO!" Goku shot up and aimed a determined glare at the kappa. "I'm not a perverted kappa like you!"

"Oh, come on, saru, the red on your cheeks tells me everything. Now who's got you all hot and bothered?"

"Nobody you sex-crazed water sprite. Not all of us think about that all the time like you do."

"But you're thinking about it now," Gojyo pushed. He had to admit it was adorable the way Goku was fighting back when it was so obvious what was ailing him. He needed a little lovin' and he needed it bad.

Goku stood up in the space between their beds as if ready to jump his tormenter and beat him to death. "I am not, so just shut up!"

But unfortunately for Goku, there was a more telling sign of his thoughts that was quite apparent now that he was standing. Gojyo's eyes flashed down to the very apparent bulge in the saru's shorts, which made his lips quirk up in an amused yet surprised grin. Damn, he thought, a kid his size's got a thing that size? It was barely peeking out at him from behind the boxers and from under the shirt, which was ruffled just so. Tearing his eyes away from the erection for a moment, he gave Goku a quick up and down. The boy had one fist clenched by his side, the other held up threateningly, and there was a glare of death radiating from his face. Well, as much of a glare of death as the saru could muster, anyway. Gojyo never thought he looked that threatening in his human form. Take that diadem of his head, however…

The kappa shuddered at the sudden thought, which caused Goku to smirk in triumph as he thought he had succeeded in intimidating his aggressor.

"Ha, feeling scared, ero kappa?"

"I see nothin' scary in here, baka saru. All I see is some punk ass kid tryin' to be tougher than he is. Kinda funny if you ask me, or maybe sad; definitely not scary."

Goku was positively growling by now, and it looked as if he was getting ready to pounce. The whole situation may have been far less amusing to Gojyo, though, if it weren't for the still incredibly apparent bulge in the saru's shorts, which hadn't lessened at all, but in fact, seemed to be getting harder. Is he getting excited by this? the hanyou wondered. He could feel a tightness stirring in his own loins at the thought, and he wondered how far this would go if he kept pushing. He hadn't had any action for weeks now, and it was true that Goku was fairly attractive. This could be a grand opportunity, but how to play it…

"So, monkey, if you're not thinking about that girl, who are you thinking about that's got your panties in a twist?"

Goku was taken aback for a second, and he saw Gojyo's eyes were not focused on his face. He followed the gaze down until he saw the bit of skin creeping out of the confines of his boxers already a little wet. He gasped and immediately turned around to hide his shame, staring at the floor and willing his erection away. It would not heed him. What had started out as stray thoughts about a certain monk had become imminent excitement as he had grown more angry and flustered with his companion. Little did he know, said companion was about to drive the nail into the coffin.

"Ooh, now he's shy, eh? Well if it isn't the girl…it's probably that sorry excuse for a monk, hai? You've been starin' at him an awful lot lately."

He didn't even see the saru move. All of a sudden, another weight was on top of him pinning his arms to the bed while angry growls emitted from the mouth of his assailant. Usually he could fight back easily, but Goku was putting a lot more effort into this fight than normal, and Gojyo knew how strong he could be. He also new that no matter what intention Goku had by attacking him like this, the monkey was still fully aroused, and he found his own arousal at a peek level as well. Since he was having a hard time using his strength against the boy currently, he decided to go for broke and use the heat between them as his weapon. He thrust his hips up sharply causing his erection to grind against Goku's. He heard a strangled gasp from above and looked up to see utter shock on the boy's face. He used the momentary lapse in the offensive to switch positions on Goku with his arms now pinning the saru down by his wrists.

Goku's eyes were wide and frantic. He started shooting his gaze off in all directions trying not to look directly at the man currently on top of him, because he was afraid what he would find there. Eventually, he felt both his wrists being held together in one hand while another grabbed his chin and forced his gaze upward to stare at the now much closer face of Gojyo. His blood red eyes were burning with an eerie fire and he smirked back in amusement at the now almost panicked face of Goku.

"You wanna play with fire, saru? Well then, let's see if you like getting burned."

I was going to include the sex in this chapter, but I got wore out. Let me know if you'd like me to continue. And for those of you rabid fans, I'm sure you have a few things to say about character and dialogue, so go ahead and say them. I don't mind.

Any flames, though, and I go DELETED!