Emma has lived shut away since childhood because she carries the Echidna, a power born once every five hundred years that could level the world in the wrong hands. Shion, one of the three Sages of the West, once survived starvation on food a young Emma gave him, and he became a mage to protect her. To seal the Echidna away, the two begin Magico, a marriage rite that sends them across the world through a chain of dangerous trials.