I love it when a story have side characters of reasonable intelligence. I know it's a low bar, but too many similar stories dumb them down so much just to move the plot a specific direction.
It's crazy how only one week has passed in their universe. You mean to say Reirin's imprisonment, trial, exile, growing of crops, learning of some extremely difficult dance, presentation of said dance, and archery all took place in this short period of time?!
I can't remember if it was mentioned before, but where are Reirin's parents? Or the emperor for that matter. There are too many unknowns to theorycraft properly.
But here's a guess anyway:
I know Kei is talking about Venomcraft, but surely body-swapping is just as rare a skill. I bet sometime down the line, someone else is going to abuse it. Besides gaining authority, another obvious use of such a skill is to extend one's lifespan by transferring from an old body to a young one.
But a bigger plot twist could be that someone has already performed a body-swap in the past and got away with it. And now they could be manipulating things from the shadows.
In fact, where are the other magic users? Looks like magic is a known thing in-universe, with that holy bow and whatnot. I'd imagine the palace, where power is concentrated, would employ quite a number of them.