Keys of Heaven

The Keys of Heaven (天国の鍵) are thirteen magical keys to allow the user to summon one of the Gods of Twelve and exclusively the Celestial Sphere Divine Spirit Tetrabiblos.

Trivia & Note

 * Named after the of Roman Catholic teaching, to which  promised to, empowering him to take binding actions.
 * This is shown during the later years of the Great War, where the being known as Christ gifted Hyland a magical key to summon Tetrabiblos to aid Hyland into battle.