The Murderer's Tribe doesn't appear in the battle / make a contribution. They are non-existent in the diagrams displaying how both sides are positioned as well.
Is this something the author missed or did I miss something along the way?
It seems strange as each tribe is meant to contribute to the war effort in some way.
I've finished LN Vol. 17 and just noticed it. Judging from the plot, I don't find it likely they'll have a chance to appear later on either