It's possible to be part-daemon in 40k? I thought they went straight to possession.
Yes and yes. See: Possessed.
I'll freely admit not knowing how 40k daemons work, but I don't think we're much like a possessed person. For one thing, we haven't gone on any rampages or anything.
And, anyways, I was showing that beacons of light exist in even the worst of settings.
Of course they do. I don't see why that's of any importance in guessing that the guys who murdered our master for little to no apparent reason are probably not going to be friendly to us.
They're adventurers. Our master was playing with demons. Do the math. At worst, it's Gray v. Black.
Judging by the name he left, they're religious types. We're part demon. They were happy to murder him just for a fairly small bit of meddling with demons that didn't even bind any to this reality except us, as far as we know. If our creation was such an abomination that he got killed for it, they're extremely unlikely to let us survive.
While we're on the subject of 40k...remember why the young Techpriests (or whatever they're called) are the conservative ones? They don't live to be old. Any party that's gotten to the level of power to succeed and prestige to attempt killing a moderately powerful mage is willing to bend the rules a little. Work with a nice part-demon, in exchange for having a part-demon pet? That's a useful tool in a bunch of potential cons.
Are you going to claim this universe is anywhere near as bad as 40k?
Aside from the way magic works, this entire story could easily have taken place on some Imperial Feudal World, and we lack any real knowledge of the wider setting, so I have no idea.
It's too pleasant to be any but a remote Feudal World, and by "Remote" I mean "Unaffected by the horror and madness of the outside galaxy".
There are a lot of planets in the Imperium, and a fairly large number of them aren't plagued by war and such, at least most of the time. Not to mention various forgotten worlds with remnant human colonists. Plus, we know basically nothing about this world. What I'm saying is, don't make too many assumptions that this is a decent place, because for all we know the guys that killed "master" are members of a church of fanatical demon-haters who would fit into the -][- just fine.
Quoting you:
"[A] fairly large number of them aren't plagued by war..."Even if this world was part of the 40k-verse, that doesn't automatically make it grimdark.