Quote Originally Posted by Falconius View Post
The demons are not existent on our world but can cross over and appear if the fabric that separates them from our world is weakened enough.
Quote Originally Posted by Jalyha View Post
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.
Putting these two lines together, it seems natural to propose that the illumination from this star weakens the boundaries between the worlds.

The gates of course would be places where such borders have become permanently broken. Some of them might be warded with eg. magical runes to deter demons from passing, while other ones might be unprotected.