Here’s an idea. A Lot of characters in the demon accords series have been explored, but one in particular still remains mostly a mystery. Elder Tsao. She rarely has anything to say and the only thing we really know about her is that she rules the vampires of Asia with absolute authority. How does she do that? What’s kept her alive and the competition at bay? Elder Senka has been shown to have a few abilities, and if I’m not mistaken elder Tsao is possibly a bit older than Senka (I’m unsure because there’s a contradiction between books).
Here’s another idea. Elder tsao and Declan become at odds. Maybe Tsao requires Declan’s aid, but uses manipulation and underhanded tactics to force him to do something he probably would have done anyway. I feel like if anyone could counter the high tech Omega (or atleast thinks she can) it would be Elder Tsao and her entourage of ancient martial artist. I some how don’t see Elder Tsao relying to much on technology.
Even if you exclude declan from my idea I feel like exploring Tsao and her culture open up a ton of opportunities. There’s a lot of mythology to be used as inspiration: Oni, Youkai, reincarnation, ninjas (vampire ninjas or demon ninjas), samurai (vampire samurai lol) the monkey king, etc. There’s so much to choose from.