Looking for an older fic where the primary antagonist is a Holy Army trying to wipe out all of the demons. They’re led, either in whole or in part by Ungai.

Hello,

the first fic that comes to my mind is To Fight In Love And War.  by Rlmpcc110511, Rating MA.

One hundred years after her return to the Feudal Era, Kagome realizes that the future she knows is about to come to pass. A war against demons has fallen on her and her group. Monks and Mikos fight against a small group of humans, yokai, and hanyou. Can they set aside their differences and work together to save the world, or will they let it all fall apart?

I'm not sure about Ungai though, you will have to check that out.
Hope I could help out!

I think you are talking about In Death, Trust Me As You Didn't In Life. Love this story.

EDIT BY WICCAN: This story, written by Kanna37, is rated MA, NO YIMs!! You can find it here: http://www.dokuga.com/fanfiction/story/2787/1

It was MA - “To Fight in Love and War” - MA as suggested by VS. Thanks to everyone for the help.