At any time there is only a single Vessel, who is the spirit of the universe incarnated into human form. When the Vessel dies, the Ragnarok Spirit is reincarnated into a newborn in a timespan of 250 years, give or take 50 years or so, who becomes the next Vessel. Once the Vessel Masters the Four Elements, namely Air, Water, Earth and Fire, and also Masters the Ragnarok State he or she is commonly noted to be a "Fully Realized Vessel".