I've been thinking about it. If their problem were due to a curse, unless the curse was given by a more powerful god, Talad and Laanx should be able to remove it. I have other theories, but I'm going to discuss the curse first.
I don't think the curse theory is correct, but it is a possibility. The power issue is mostly self explanatory, and Laanx and Talad are some of the younger (youngest?) gods, so they can't be expected to out-power the more experienced ones (they couldn't even use magic until Vodul taught them, for Jimmy's sake!). One glitch is whether you can put that much power into such a simple curse. However, if Laanx cursed Yliakum with little effect (that I can see), maybe a curse isn't such an easy thing to do. Or maybe a curse isn't something you "put" on someone, but something you "hold" on them. As in, the god that cursed them is actively maintaining it, so to reverse it would be like removing a wrestler's hold on somebody and then keeping them away until they give up or are defeated, as opposed to unlocking a jail cell.
Another possibility is the biological or spiritual sensors that normally detect a god's presence and feel soothed, protected, or empowered, or else disturbed, frightened, and weak (depending on the god), could be reversed in the Diaboli. So the force normally perceived as soothing actually disturbs the Diaboli. The force itself doesn't have to be good or evil, just a type of magical or spiritual energy, similar to how there are magical ways. Like if Laanx and Talad operate on one magical "frequency" range, and maybe some other gods operate on another. Those other gods would probably disturb the other residents of Yliakum, but be soothing to the Diaboli. It could be a "sweet-spot" or a "sour-spot". What I mean is that maybe the particular "frequencies" that are felt as soothing are just one small range and the rest are not, or the other way around. An example of the latter is that certain audio frequencies annoy me much more than others, sometimes to the extent of causing pain (either to me or the source
). Meanwhile, other people don't notice.
A third possibility is that the negative effects are due to the Diaboli's own practices. Maybe they indulge in some form of magic that makes other magic hurt them. Or maybe they are filled with a type of magic that causes pain or sapps energy when displaced. What that means is they are normally filled with "x" magic. If they attempt to wield or are hit by an object with "y" magic, some of the "y" magic is transferred to them. For this to happen, some "x" magic would have to exit them. If the "x" magic hurts them as it leaves, then we have a solution to our problem. Well, a partial solution, because the reason they are filled with the "x" magic hasn't been revealed. It could be a way to keep them loyal (either to their god or their form of magic, or the dispenser of the magic). Or it could be that that type of magic has some benefit to outweigh the cost, such as their "gorgeous, perfectly shaped bodies" and charisma. I'd be tempted to say that it helps their resistance to elemental spells, but that is supposidly from their "deep knowledge in that area of magic". It could be a contributing factor though.
Also with that last possibility, maybe their society or the god(s) they didn't give up punishes them for hanging around temples for other gods. They'd avoid those places, because later on there would be a good chance of their suffering. They could even be disowned or executed for such an infraction. That doesn't explain the susceptibility to holy weapons though.
A more remote possibility is that they distrust the gods, possibly from some previous letdown, thus their discomfort in temples and such. The effectiveness of holy weapons could be due to a kind of "placebo effect", where they believe the magic will harm them and because of it their bodies' defense systems weaken. Or they could loath such items so much that touching one has a deep psychological impact. It doesn't say that the holy weapons do physical damage, just that they are "devastating against them". The devastation could occur when contact with a holy blade causes the Diaboli to have involuntary shudders, or even just become distracted by the idea that such a thing just touched them. The effects could begin even before they are hit, with the knowledge that the opponnant is using a holy weapon eating at them and making them act with less (or too much) care.
I agree with the argument that the history is supposed to be fact (though possibly unknown IC). I have trouble accepting the statement about them giving up a prior god though, because it can technically be read and intended to be either way. Yes, it could (and should) be clearer, but that could be human error. Just look at the even more blatant errors. I'm not arguing it either way, just saying that you probably shouldn't give much weight to it unless the writer clarifies the issue, because it is a very easy mistake to make.
Along the lines of what is fact and what isn't, the bit about their homeland being a "burning land...." is actually "A popular tradition". The history doesn't come right out and say what the place was like, just what a major in-game theory is. That part really doesn't matter, I just thought I'd mention it. It's the next part that matters slightly (and only slightly). In that same in-game-theory way, it says that "Some sages believe they originated in a distant, unexplored universe", which could lend validity to the ideas about the "magical frequencies" or exotic forms of magic, if those sages are in fact correct. Like I said, not very important, but something to think about.
Personally, I think the Diaboli distrust the gods and prefer to be independant. That is more in-tune with their character. They probably lived on some world torn by inter-god wars, where they were used as pawns. The descriptions of their world could stem from the world-tearing effects of such a war, and the blood of the innocent casualties. If they had to be very cautious there, it would also account for their view of Yliakum as a paradise and their tendency to not settle down. The loss of life could also have impacted their rather free way of making new Diaboli and Ynnwn, because they would have needed to replace the casualties. I attribute the effectiveness of holy weapons to my "frequency" theory, specifically the "sour spot" version, which goes in with the distant universe idea.
In that case, a Diaboli could follow Talad, Laanx, or the Black Flame (if he/she knows about it), but there would be the risk that the god's power would harm them, and the risk that the other Diaboli would disown them for associating with a god. Both may be more than that particular Diaboli can take, which means only the strong ones (or the ones that enjoy misery) would worship Yliakum's gods. If they did, though, they may recieve better treatment from the god itself, because of the sacrifices they are making to support it.
Well, that's my two tria. Let the non-childish, well-thought-out tearing-up begin. Though the childish stuff is good for a laugh once in a while
