I have been wondering if they might be extensions of each other. Now, much of it could be just me--I tend to lean towards particular systems of magic and religious views --but I also wrote both series. Here's what I did in both:
- In The Luriel Cycle trilogy, magic comes from the world. Several years before, I did the same thing in the Demon Age novels, particularly Spirit Blade.
- The Black Fire demon in Spirit Blade resembles the daemons of The Luriel Cycle.
- In both, the life of the worlds are the sources of magic.
- In both, the worlds gain sentience because of the accumulation of life essence. However, in the Demon Age series, that has been the case for thousands of years. In The Luriel Cycle, the nuonir of Fal Oroneth only gained sentience when the Un'dei exploded. The Un'dei was the sentient power from a completely different realm.
The Ancients of Derandria (Demon Age) and the Falluar of Fal Oroneth (Luriel Cycle) were both mysterious, until the Falluar are exposed in Eternal. We don't know yet about the Ancients.
And then there's the Nik'Terek gate of the Demon Age series. The gate was supposedly created to rid Derandria of the mistakes of the Ancients. However, I've always speculated that the gate was actually a portal, which means that the Obelisk of Mai'Kari and the demonlords who passed through, among other things, were actually transported to another universe or world. In Eternal, Lilly explains to Commandant Renvil that the realms could be considered to be different universes. The Falluar visited multiple "realms" in their explorations through the bridges they created. What if the Nik'Terek Gate was actually created by the Ancients of Derandria and that it only later came to be known as the Nik'Terek gate because the Nik'Terek demonlord clan took over responsibility for it? But the gate is a one-way ticket, that could have linked to another realm and world, like Fal Oroneth in the Shadow Realm. Remember, time is different in different multiverses, as explained in The Luriel Cycle trilogy, so anything is possible.
These are the thoughts going through my head at the moment and ones which I find quite interesting. I like the idea that the two worlds are linked but separate. It makes my expanding universes that much more intriguing. It means there is a larger plan in the works that not even I yet understand but is unfolding in its own time.
If these worlds interest you, you can find links to purchase both series at my webpage at melanienilles.com.