Keystone Gate is a giant composite structure two kilometers in diameter, located at the center of the island. At twelve stories, its aboveground section was the tallest building on the island.
- Within the facility were government administration offices, including city hall, and numerous hotels and commercial facilities built one after another, functioning as the island's nucleus.[1]
- Keystone Gate has 40 levels beneath the surface, and is heavily defended by a battalion of Island Guards along with dozens and dozens ofmagical defences and barriers.
- It was designed to absorb the effects of ocean currents, wind, waves, and so forth, such as bending and vibrations between the Gigafloats. Without it the four districts of Itogami Island would suddenly collide, or perhaps break apart, drifting atop the Pacific Ocean.
- It was a critical facility, truly worthy of the name keystone