mentions on the demon god
First mentioned as wanting a shard and that 'he' would not come out of the gate without it, I think I heard somewhere that the mask and hairdecorations Kharla wears then is supposed to represent what they believed the demon god would look like. Kharla seems to want to bring it over, I suspect that's largely due to Senekha's influence.http://www.drowtales.com/mainarchive.php?sid=463
It was originally Senekha's scheme to rule the world. She talks about the plan here and a little of what the demon god is, shortly before she's executed.http://www.drowtales.com/mainarchive.php?sid=5263
Ni'bai is after Senekha's notes, she's taken the shard and she just wants to summon the demon god in the name of vengeance and destruction of everythinghttp://www.drowtales.com/mainarchive.php?sid=7411
I'm pretty sure there's a few more mentions here and there, reminding us about Ni'bai still existing and plotting but I'm too tired to look them all up at the moment. They pretty much just hide away biding their time, feeding up the shard until kiel slips up years later and they get access to Kharla. those links show pretty much all we know about the demon god before it's summoned.
There's a lot of speculation going on of course, there always is. I don't personally believe it's linked to Sharess at all. I find rereading the comic when confused to be the best option. It's just been going on for so long you're bound to be confused by some things if you don't.