Also, why aren't there any negative numbers yet?

And lastly, what's the time period of the existing humans?

S.Ex.N. is in many ways similar to an Earth environment because it essentially copies the nearest reality they originated from. As a number does its "job" by being included in counting sequences, mathematical theorems, being the quantity used to describe an arbitrary pile of pebbles, w/e, it becomes more aware of the reality describing it. Over time, the dimension the numbers find themselves in serves as basically a smudged carbon copy.

This isn't a perfect analogy or timeline either, but just something that happens to be. When Zero and Two met, it was after a majority of humans began to adopt zero as a number and mathematical object at the same time "Arabic numerals" were becoming popular. But nothing explicitly demonstrates that Zero and Two are reminiscent of humanitys cultural or stylistic trends at the time of this boom hundreds of years ago.

Humanity has a time stream that just continues forward, but in the number line they can pick and choose from any era in Earths past to find one to duplicate and be influenced by. There probably were times in the number lines past where things seemed less "modern," and it just so happens that right now they collectively feel the current trend is late 20th to early 21st century, and is just the most convenient fashion. The current time period for humans? It could be right now for all I care.

As for what they ARE, yes, they are in many ways "humans" and act and think like them, but unlike humans they are personified to represent the being with which they are. So Six for example is the epitome of everything that makes six "six" which includes her parity, prime factors, the history of how the numeral looked to other people, etc. You take all that and give it sentience, it will start resembling a human being in some ways, and then once these beings begin to search for purpose beyond the day to day hassle of semi existing, she puts on cute dresses and learns to play the cello.

zero and the other numbers all inhabit the same lil pocket universe, and were formed into existence as soon as a majority of humankind recognized their numerousness. the essence of each number, its "itness," is what birthed them into self awareness.

because zero did not formally mathematically exist until he was unanimously agreed to by the rest of the world, the memory of his origin is much more nuanced and cloudy, only observed by a select few civilizations. while other numbers were formed on the basis of counting, zero specifically had to be invented, thousands of years later, making him the youngest of his peers.

im very glad you asked

Ex Nihilo exists in a world somewhat adjacent to the reality we inhabit. Sometimes the dimensions intersect, sometimes theyre separated, it really just depends on the fluidity of whatever makes the most sense at any given moment.

The abstract notion of quantifiability led to counting and numbers, and in E.N. i like to show the little world that whole numbers (specifically 0 through 9) would inhabit if they were indeed real people. though this can lead to many mathematical types of jokes and interactions, i really kind of just enjoy having a cast of characters i can play with to express my feelings and thoughts, so i think its fun to not only treat them as numbers, but also just ordinary people who just inhabit the same lil pocket universe. before humanity existed, or even life, there existed objects that could be counted, but by whom? did a grouping of five pebbles still have the same "five-ness" to it if mathematics and numbers were not yet discovered by man? maybe it did. maybe that aspect of existence was waiting to spring forth into being, and once it could, so did the numbers come up. the five pebbles were counted, and once they were, so Five was born. were they already born and just lying comatose and dormant? whos to say!

zero (me!) is the absence of positive or negative quantity, the operator of the additive identity. he feels unique and special because of the qualities inherent in being a number unlike any other. as the most recently discovered number among his friend group, zero is technically younger than everyone else

i always drew zero with entirely filled in black ink other than his eyes to represent his difference to every other number, who all usually have blank white characteristics

in every comic with zero, i always wanted to portray a theme of loneliness and isolation, a topic i explore and think about very regularly. even with all the friends zero has, sometimes he feels happier and at peace being by himself. and in spite of that, sometimes he just wants to feel normal and hang out with someone so that he doesnt have to feel lonely anymore.