[HoneyBadger]

It's thematic in the sense that wristwatches don't grow on trees.

Yes, you've got magic going, so you can say that anything is possible, but fully armored human soldiers don't just pop up out of the ground and fight for you. You might as well expect a crop of AK-47's. Kappas, on the other hand are 1: demons, so they can have magical origins, and more than one origin, for that matter, and 2: they're reptilian, so it makes a lot more sense that they come from dragons' teeth than humans do.

And yes, it's important for magic to make sense, because magic is powered by belief. Infact, Thaumaturgy is all about things making sense-you do something on a small scale, and a large scale thing happens, or you do something similar to what you want to happen, and what you want to happen, happens.

Magic isn't science, it's not governed by strict laws, but it has rules, conduits, and structure.

Now I know all about the legend of the dragon's teeth. I've read it many times, and yes, it says fully armored soldiers sprang up out of the ground after the teeth were planted-but kappas *are* fully armored, and we're dealing, basically, with the impressions of ignorant tribesfolk here. If they saw a kappa, with their shells and distinctive heads, yes they'd probably recognise it as a "fully armored soldier".