This came up on /r/worldbuilding from time to time, mostly “how do races of vastly different size coexist?” but it can be equally interesting considering how very large or very small races would go about things once you at least nod in the direction of the square-cube law.
For example, someone the size of an insect can shrug off falls that would kill a human when scaled to our size. This would naturally effect how they build their buildings. Tall towers could have doors open to the street below, and people could just jump down.
I considered a scene like this when writing this post. Some exhausted clerk working on an upper floor of a building ends his day by jumping out the window. Sunbeam interprets this as him attempting suicide and catches him midair, then gives an impassioned speech about how life is worth living and how he has friends and family who care about him etc, only for him to angrily interrupt her mid-sermon to tell her off for making him late.
Water also acts differently when you’re small enough. You see this in movies like A Bug’s Life where they don’t need cups when drinking liquids because the surface tension holds the liquid in a bead that can be held on its own. I wonder how they’d handle large bodies of water; how boats would work and so on.
Looking in the other direction, a bigger creature has a bigger appetite, which has serious logistics issues if a larger creature has to be housed by smaller ones.
This is addressed in Gulliver’s Travels when Gulliver visits Lilliput. He’s housed in an old temple, given vast quantities of food, and has attendants who carry away vast cartloads of what’s left after the food is digested.
Going back to the issue of fall damage, at a certain size even a trip would be fatal.
As for species of vastly different sizes coexisting, Zootopia comes up a fair amount when this is brought up. When I first watched the movie it occurred to me that the rodents must have a huge financial advantage over larger animals because they have smaller living spaces, eat less food, have lower electricity consumption due to heating and lighting said smaller spaces, etc.
This seems like it has a troubling corrolary. What job can a giant do that’s valuable enough to a small society to justify their relatively massive needs? It would be pretty tragic if giants were on the verge of starvation all the time in order to be “civilized” in a fantasy society. I feel like there’s a ton you could unpack there.
Smaller races pay larger races for protection.
Construction in a world like that is an industry requiring all sizes. Larger races moving equipment or materials, smaller races would make great electricians and plumbers, for example.
My favorite: 3 Giants Move U™ a moving company specializing in moving your entire house.
I sort of address this in the story linked in the OP. Sunbeam is a sort of reverse kaiju in that she builds infrastructure rather than destroying it.
An alternative scenario was that Sunbeam is a huge rail enthusiast and squees with delight upon seeing the bugs’ train system (I originally thought of the bugs as being at a late Victorian tech level but that didn’t come through in the story). Because of their small size the trains are like models from Sunbeam’s perspective and she completes a bunch of transport infrastructure projects as though she were playing with model trains.
Another idea was Sunbeam casually munching on berries she picks from a bramble near the bugs’ town. This raises the ire of the townsfolk because they’re growing the berries as a staple crop and each one she eats could have fed a bug for a day.