Erna

Erna is anti-mana, the very essence of monsters. It gathers in the depths of the earth and feeds the underground labyrinths, which grow along with it; everything in the labyrinths is steeped in it and its miasma.

To contain Erna, Syril invented the Erna-gathering system thirty years ago, drawing all the world's Erna into eight devices, the greatest of them in the city of Erin. The labyrinths and this system together keep the world from an excess of Erna.