Given the usual level of activity inside of a gym, one might have been forgiven to not paying much attention to a particularly small, slim, even cute-looking gym-goer. They were clad in a typical set of gym clothes, and were short enough compared to just about every other man in the gym that they were almost literally beneath notice - perhaps five feet tall, on a good day. At the same time, this lack of attention meant that nobody quite realised that this newcomer had never actually entered the building - they simply exited the changing rooms at one point, fully clothed, with no lockers reserved in their name and no belongings left behind. It was almost as if they didn't exist one moment, and came into being fully formed the next - though, of course, though nobody would realise it for a decent amount of time, this strange little figure was Arceus, the creator-god of all reality, here to have some 'fun' with the adorable little mortals that lived within his domain.
Perhaps the only other clue that something was amiss with Arceus, as he entered the main area of the gym, was the look in his eyes. Nobody that small should have been anywhere near as confident as he was - nobody so thin and reedy and weak should have worn such a subtly-smug, almost smirking expression on their faces. By the same token, nobody so small in every possible way should have had such an odd gravitas and presence to them. But with everyone in the building already concentrating on building up their own muscles, Arceus went unnoticed - at least, that was, until he chose his first lucky (or perhaps unlucky, depending on one's perspective) worshipper-to-be.
"Man, who let a shrimp like you in here? I don't think I've ever seen someone so small and thin walk into a gym!" A deep male voice speaks above Arceus. Looking up, Arceus saw a rather impressive specimen of a Machoke towering over him. He was about as big as a Machamp, so Arceus was certain if they evolved they would be even bigger than average.
"Hello! A pleasure to meet you. I'm relatively new here but I'm certain I'll make gains quick enough to reach your size even!" Arceus says with a smiling confidence. The Machoke is silent for a moment...before he just starts laughing loudly.
The Machoke's oversized chest visibly pumped and deflated with every breath he took, and the sound of his booming laughter attracted more than a few sideways glances from other gym-goers. Even if Arceus hadn't been a literal god, it would have been obvious to him that this Machoke likely ruled the roost, as it were - the alpha male of this gym, or perhaps just oe of its most frequent patrons. It was easy to see why, with the thickness of his arms, with his dense and powerful core, his bulky neck - though, of course, Arceus also knew that even his current small, cute, weak body would have been capable of folding the Machoke like a lawnchair without the slightest hint of effort.
"WEll, little guy," the Machoke said, chuckling loudly as he bent down - very, very slowly bent very, very far down - until his nose almost touched Arceus'. "Why don't you show me what you can do? I get there's a couple of one kilo weights over there," he said, visibly shaking with constrained laughter as he pointed over to the weightlifting area. "I bet those will give you a good workout!"
Arceus, looking the Machoke in the eye, without any hint of anger and the slightest tone of smugness, said. "Well, that does sound like a good place to start out at!" And with a smile, he walked over to where the weights were located. Looking over the rack, he found the weights that weighed about a kilo. He then picked them up with no effort, and began curling them. The gym goers who were watching because of the Machoke's outburst couldn't help but watch in total awe. And their awe only grew along with Arceus, as with every curl his body and muscles surge larger and larger, a few inches at a time.
The Machoke himself didn't pay attention at that point and was currently doing some stretches and flexing routines, to show off his muscles to the others. He got annoyed though when he noticed they no longer watched him and seemed to be fixated on something behind him. Only then did he turn around and saw just what had grabbed their attention. Only to find that the little guy from before was bulking up and curling the kilos with ridiculous ease, that he was going to grow bigger than the Machoke!
Of course, Arceus' growth wasn't lightning-fast - he wasn't anywhere near the Machoke's size, yet - but his growth was still rapid enough to not just be noticeable, but to be undeniable. With every left of the weights, Arceus' arms visisbly tensed, pumped, and swelled larger - his abs rippled and shifted, both multiplying and growing larger and denser - his thighs and calves thickened and bulged, and his neck swelled out wider, bigger, causing his high-pitched grunts - exaggerated, of course, because Arceus was expending no more effort than he would when breathing - to deepen a bit at a time. His frame steadily swelled an inch or two higher with each lift, with each pump, and what had started as just a single confused, wayward glance had quickly turned into the entire gym watching in stunned, awestruck silence. His top began to grow steadily tighter across his thickening, growing torso, only making his inflating muscles seem all the larger as it tugged up and up, showing off more of his powerful core with each new growth spurt. By the same token, his shorts were tugged up further and further - not only showing off his increasingly powerful legs, but also a bulge, which was itself visibly lengthening and thickening with every flex, with every pump.
If one was only looking at Arceus' expression, one might have thought that everything was entirely, completely normal - though, to him, of course, this was. This increasing size, this growing level of strength - others standing worshipful and awestruck in his presence. It was of course, then, no surprise when Arceus gave the Machoke a wink - still looking up at him, but easily a foot or even a foot and a half taller than he had been mere minutes ago, and surely twice his previous weight if not even heavier, purely down to his increased mass - and dropped the one-kilo weights. They barely made a sound, but in the fearful, stunned silence that reigned over the gym it sounded like a thunderclap. Arceus licked his lips, and smiled innocently, and...