It's Homo Time! I mean-

Example: Ben has canonically pulled several consecutive all-nighters, interspersed with extremely short naps, which means he's gone upwards of seventy-two hours with less than three hours of sleep. This is on the upper end of what humans can endure without having an extremely severe impact on their functioning, but it's heavily implied that he and Gwen (and probably Kevin) are desensitized to sleeplessness.

Now, do I think there are alien species that can go a long time without sleep, or maybe even ones that don't sleep, in the Omniverse? Definitely! But there's a big difference between someone who doesn't sleep much because of their biology and someone who doesn't sleep much despite their biology.

"My kind doesn't need to sleep much. I've been awake for a week and could go a few more days still." "Oh, cool. Humans are supposed to sleep for eight out of every twenty-four hours, but I didn't have time to sleep last night, and the night before that, I only got about four hours. I should be fine as long as I get a nap in before tomorrow, though." "...W H A T ???"

Another thing that I think is really relevant? Human stamina.

Like yeah, sure, all these alien species have super-speed or super-strength or flight or what-have-you, but what's always made humans weird is our stamina. Hello, persistence predators.

So I have this concept for a scene. Basically, it would be a story where Ben gets taken over by some sort of mind-controlling alien parasite. The parasite isn't fully sapient, but it has the drive to do something — feed or mate or whatever. It doesn't have its own consciousness, but it overtakes Ben's consciousness, so basically, everything Ben does under the parasite's control is entirely from his own mind, just laser-focused on a goal Ben himself doesn't have.

And of course, him not being in control of himself, he wouldn't be as inclined to lie or mislead as usual.

But Ben doesn't know if the parasite could survive an Omnitrix transformation, and the parasite doesn't want to die, so he's stuck in human form. And Rook, of course, is confident that he can take his human partner in a fight.

Right?

Wrong! Rook's biology is optimized for speed, strength, and agility, which means every last motion takes a hell of a lot of energy. Ben's biology is optimized for stamina and has a decent amount of those other things, which means he can, if only just, hold his own against Rook... but he can do it for a long frickin' time.

They're isolated in some way (because of Ben plotting, probably), so Ben has all the time in the world to wear down his partner. And of course, without his usual filter, he'll tell Rook exactly what he's doing.

"You know, a human can last three days without water before their body starts giving out. How long can you last, partner?"

"I can go seventy hours without sleep. You're basically a space cat, so I'd be willing to bet you need a nap soon."

"Did you know humans evolved to tire their prey out? My distant ancestors hunted lions over the course of miles, never letting them sleep, until they couldn't keep going. Gwen told me that."

"I don't blame you for thinking you could handle me. I wanted you to underestimate me. That's what I want everyone to do. No matter how much I trust you, there's always a part of me preparing for you to betray me. It's nothing personal — just a hazard of the stupid watch. Being hunted for years makes you wary, y'know?"

and so on.

...anyway.

Let me explain:

(I'll be disregarding the hardcore proship options, since I'm not interested in writing that)

Option One:

Their relationship progresses similarly to canon. It leans a little bit more into the "coworkers with wildly different personalities" option, and it stays that way until Ben is Ben 10K. They have a long history, but they're not really close. Azmuth begins to interact with him more, now that he's accomplished so much. Him becoming such a highly renowned hero was enough to get Azmuth out of his shell — seeing his creation being used for so much good is enough for him to bother interacting with the person using it that way, y'know?

Ben has a lot of confidence, and he's level-headed. He's been around the block by now. In a lot of ways, he's a completely different person than Azmuth met when he was younger.

(Humans have a very different conception of ages than Galvans do. Just based on the "Blukic and Driba go to Are 51" episode, I'd say it seems like Galvans change physically a ton and mentally barely at all, while of course we know that humans change physically quite a bit and mentally, also quite a bit. So it probably wouldn't occur to Azmuth that the difference in personality was due to age; he'd probably assume it was purely due to excessive combat experience.)

In any case, Ben is still a little shit, and he makes a point to annoy Azmuth as much as possible (see: Ultimate Ben 10K). Azmuth finds it irritating at first, but he eventually comes to appreciate the familiarity with which he's addressed, and frustration gives way to appreciation, which in turn gives way to a sense of closeness.

Ben, in this story, would have some pretty mixed up feelings about Azmuth. If there was any element of attraction, he'd be weirded out at first. But mostly, he likes the guy.

In this scenario, their respectively isolated/elevated social positions would put them in a position of not really being understood by anyone else. Ben may or may not have a partner, but polyshipping would actually make this better lol.

Basically, they'd have a weird little QPR, starting when Ben is nearing middle age, where they're life partners almost entirely on account of the omnitrix inextricably binding them together. It's part of Ben (see: genetic fusion), and it's part of Azmuth (see: his greatest work), so they're stuck with each other one way or another. It's just lucky that they get along, and eventually (about when Ben's human age catches up to Azmuth's Galvan one), they have a weird little romance.

It almost feels like an inevitable progression of their friendship. The closer they got in age, the closer they got to being an old married couple (coworker dynamic, then friends, then QPR, then romantic). Soon after they reach that point, Ben dies. Azmuth grieves him, of course, but there's a sense in which it just feels like part of that progression. Ben aged faster than him, so he was always going to die first.

Option Two:

AU where Ben and Azmuth don't meet until Ben is well into adulthood. They have a weird, tense relationship. Ben has been fused to this device for over twenty years, he's made an intergalactic name for himself, and he's even saved the planet in which its creator was born, but its creator hasn't bothered to even introduce himself, let alone help with any of the technical problems over the years.

He gave up on meeting the Omnitrix's maker a long time ago, so when he finally does, he doesn't really give a shit what he thinks. Azmuth, though, is torn between lingering resentment about the Omnitrix being used as a weapon in the first place... and a sense of immense pride and gratitude, considering how much good Ben has done with it. He went through the process of "wow. fuck. the universe can die actually" -> "okay, maybe it doesn't all have to go" -> "this wielder of the Omnitrix... has actually convinced me this universe is worth saving" without anyone witnessing it, and without ever directly seeing/meeting Ben, so he has the sense of Ben saved him by being Ben, but not the rapport that he has with Ben in canon.

But then they both get hung up on the fact that they understand each other, despite only just having met, in a way no one else can. They've been inextricably entwined for decades, and they've only spoken three times, and their senses of identity and fates are interdependent, and Azmuth's creation is part of Ben's body. And they don't really like each other that much. And they irritate each other on purpose, which doesn't help.

By the time they get to the point of not wanting to punt each other across the nearest solar system, they're weirdly codependent and obsessed with each other, and they have a weird-ass rivalry-style friendship for like fifteen years before one Ben goes "oh shit am I having xenophilic thoughts?" and Gwen's eye twitches because fucking obviously, Ben, did you think your arguments about control of the omnitrix weren't kinky banter???

And then when he tells Azmuth this, Azmuth freezes for like three minutes and then is like "well we don't have to worry about getting married, since we're already bound, body and soul, by that device on your wrist. it could probably be shifted to look like a ring, even" and Ben has to resist the urge to throttle him.