The Twelve Apostles (十二使徒 Jūnishito) is a group of twelve high-ranked Angels in the White World.
Z/X Encyclopedia Entry
Among the Angels in the White World, these are the most exalted of their number due to their incredible psychic powers. The Twelve Apostles are among the highest ranking angels, second to only the Four Archangels. Each of them waits for a chance to take the position of the Archangels.
The Twelve Apostles lead a host of Guardians and Angels who are comparable to the population of modern nations, and naturally, they look down on most people for lacking psychic talent.