The Amatsu twins begin to grasp the deeper meaning behind their spiritual training when ominous beings from another realm surface to sow chaos among humans. Under their grandmother's direction, they discover their family's historic duty to repel these intruders and safeguard a sacred bloodline. The sisters soon receive their first assignment to watch over a young man of divine heritage, whose unpredictable conduct adds unexpected complications to their role. As threats close in from multiple sides, Ai and Mai must draw on their abilities to maintain balance in a suddenly perilous world.