I like Azelor's idea about the second star that's sometimes in another plane/dimension/whatever. I think it could tie in nicely...
Like the movement of the star affects the node network, or disrupts the death-energy-whatever from the GTH concept, so that demons are more or less prolific depending on when the star is visible.
That would also give lots of leeway in the storylines available (if someone *really* didn't want to incorporate something, maybe it's because the star is gone (or back!))
Plus, it's just cool as all get out.