The Demon Realm. The Two Realms Teleportation Gate. The ruins of the former European Union Harmony Bureau fortress.
This place should have been a heavy-firepower fortress, teeming with all kinds of cutting-edge weapons of war designed to fend off massive Magical Beast assaults. It was impregnable, like a steel bastion rising from the Black Forest, utterly impossible to breach from the outside.
But the Spirit Summoning Association had captured the fortress's teleportation gate on the Earth side and broken in from within. Furthermore, they had a member who was an exceptionally skilled hacker. He manipulated the network and detonated the entire Harmony Bureau fortress, along with its armory, reducing it to the current ruins of black ash and scorched earth.
