It looks like it's a coming-of-age story about a young, kind but ultimately inexperienced prince caught up in an invasion of his home country. It's set in a fantasy version of Persia, so far there hasn't been any high fantasy stuff popping up, a lot of military drama topped with some interesting political and religious conflicts. For something that's supposedly an adaptation of someone else's novel, it actually matches up with some of the themes in FMA, which I was a bit surprised about.
I'm really enjoying it so far, especially as a history geek! There's a lot of love for medieval Middle Eastern history poured into it, both in the writing and in the visual details, like the embroidered robes and armour.
FMA's entry on TV Tropes' Better Than It Sounds page:
Military specialist searches for a magic rock recipe to get his brother out of a can. In one version of the story, the rock is their father, in the other version the rock is us.
Or: Children see a Thing Man Was Not Meant To Know, run around country looking for another one.