Fantasy or Sci Fi Book series, at lest 3 or 4 books, set in an alternate reality with angels and demons living alongside humans and a fallen angel turned assassin helps the H

[Ryan]

I read this book series sometime before college so it had to be out fully before 2013. The writing seems likely it was from after 2000 but I can't be sure since my memory is so foggy. I remember that one of the titles either that the work 'clock' or 'gear' in it.

Plot wise I can't remember much but I know there was a H that was male and two women that were working with him. One was a childhood friend and the other was I believe a fallen angel made into an enhanced assassin.

Big parts of the story that stand out to me is that there was an army of demons marching to war. But the only way they could walk on the ground was if it was soaked with blood so they were mass sacrificing prisoners to advance. We had a POV from one of the prisoners who was a traitor to the humans that the demons killed. The other is that there were massive Gundam like robots that were powered by souls trapped inside of them. And they were completely indestructible because the soul inside them was convinced it was entirely indestructible which made it true. I think their reveal was a large part of either the second or third book.

I also remember that the first book opened with assassins trying to kill the fallen angel that helps the H. She had left their order and was on the run. There were many and she was easily killing them all and the line that wrapped up the chapter was something along the lines of: 'they died silently just like they were trained'.

I cannot for the life of me remember any more than this and would love to re-read the series. I don't believe it was a YA book but as I said it's been so long it may be. Clearly these details aren't reliable to google so I'm hoping someone here can help me remember this.