Talking about enemies is one of the most obvious crossover between game mechanics, story and art. All of them are equally important to form a good antagonist, that is fun. To me, it also means the disciples are influencing each other as well.
Minerals of Plot
I've read the guide to bad plots(http://www.ansible.c...le/plotdev.html), I tried to not use plotdevices, but I almost have to have at least one in a game like this, I just can't get anywhere without one. BEHOLD: The Minerals of PLOT!
I cleverly call it Diabolite. The name is not the greatest of all, I know. I am likely to change it when I find a better one. For now, it will serve it's purpose.
And since I am already writing about names that are subject to change, I let the humans call the enemies "the Horrors". The name doesn't satisfy me either, it is a better way to refer to the antagonists than "the enemies" or "monsters" I presume.
But back to the Diabolite:
the minerals come from far down under the earth: Natural Diabolite grows in a crystal shape. Even in it's unrefinded state, it is a valuable resource for both the Horrors and the Rising Sun. The Diabolite crystal is remarkably sturdy against most steel alloys. It tends to enclose precious metals like Titanium, Gold, Cobalt, Palladium and sometimes even Platinum that can be retrieved by refining the mineral.
But it's main application is to serve as a source of power for the humans as well as the horrors. Since the invasion, the humans have almost no other powersource left.
For the Horrors, it is more accurately described as a nutrition, the more primitive Horrors seem to feed on the raw Diabolite, while refined Mineral is eaten by the more intelligent creatures. Either way it is the only thing left after defeating one of the Horrors.
More on the mechanics side:
Diabolite is the main mineral of the game, the player needs it at LEAST to buy ammunition. Maybe I will do more with it once I give more thought into the Items/Skill system.
The weapons of the later game mainly use high performance ammunition. While effective, using them is also expensive, using it against a weak target is essentially wasting resource.