Your idea has merit but part of me says that making the narrator a character doesnt strike me as good. He should stay 'faceless'
how about...
"A young refugee stammered about a maniac from his home village who thought to stand against the Myrkridia. He and the rest of his family had made their way to Muirthemne over the following weeks only to be eaten alive within sight of the gates. When we arrived at the village, it still stood, their leader a bear of a man stood strong against the Myrkridian devils.
I like the idea of Myrkridian bands they would be nomadic going across the land lead by the more closer to human intelligence myrkridian giants (I imagine normal myrks being a bit... not so smart) Perhaps killing for food from each village they got to but leaving them alive, threatening death for the whole village if they resisted. Perhaps the leaders owe moagim (I don't like them having an honor debt) fear moagim, or are otherwise beguiled by moagim to organize them into a fighting force to take on Muirthemne
