Thank you, Unice! I'll let you know for sure.
Rhodeworks, if I can address some of those points, (because they're fair!) I think a big issue you're seeing is I didn't provide a lot of details, knowingly. This was meant to be simply an outline, and a general idea of the plot. I can provide the details you asked about though!
1. Keldaxus, I considered basing off an actual demon in biblical mythology, because everything else in the story is, to some extent or the other. Given that the story is Dax's, I felt that making him unique in not basing him off an already existing character was important to the narrative. As for his name, changing it is something I'm open to? If people think it's too generic and villainous? Razekial IS based off a mythological figure, I simply didn't base his name off of it. That's also something I'm open to altering.
2.Keldaxus is a demon in crisis, though he doesn't show it. He's dealing with feelings like guilt, sadness, and affection for the first time in his existence, although the feelings are fleeting and very dull when we first meet him. He doesn't know why this is (I do, he does not), but that is explored in the story. As for the questions presented, Keldaxus knows what he was told, but Lucifer reveals himself to be less-than-forthcoming with information, even to his lieutenants. Dax realizes fairly early on in the narrative that he never knew nearly as much as he thought. He was very much a disposable tool from the start. However, things he DOES know, and that he can confirm are true, from personal experience, are vital to the mission of the Children of Abel. Which is why he's considered important to their plan. Why not a different demon, I'm sure you're wondering. And if you weren't, you are now! Well, there's a couple reasons for that. First, put simply, Dax is fairly powerful. There are billions of demons on Earth when the story opens, and many are shown to be flawed in large ways, on an individual level. Few demons possess intellect of any notable caliber, along with strength or power. It's typically one or the other. Their power came from their numbers. The other reason, even being deceived as he was, Keldaxus has plenty of still-useful information. Notably, who the Seven Sins are, where they like to hang out, and what their weaknesses are (in most cases).
3. I'm actually really glad you asked that! While this book focuses almost solely on Christian and Jewish mythology, the canon of the universe as a whole is the suspended belief that every religion and faith has a root in something real, that's been lost since the earliest days of humanity. In fact, Heaven and Hell are both realms within Ygdrassil in my expanded canon (still in early stages, but it has its bones). Christian and Jewish mythology takes center stage in this narrative, but other things are out there.
4. Quite different, but this also brings up an interesting detail. After Hell wiped out enough humans to basically ensure any mass resistance (the way I have it now, about 8% of the human population survived, which doesn't sound like a lot but is about 612 million people), demons stopped going out of their way to hunt humans down. Are they a threat? Oh absolutely, but their goal seemed to switch gears from extermination to... something else, around that benchmark. Humans don't know what, and most frankly don't care. Humanity now mostly exists in isolated settlements along coastlines, in deserts, mountains, and other remote regions.
I also want to clarify that the story contains a lot of internal conflict for Dax. He has to make a lot of difficult choices, question what few beliefs he has, and essentially choose (major spoiler) between allowing rampant chaos, or saving a world that he knows will always revile him, but that over the course of his journey, he sees things worth saving in.
I hope that clears some things up!