In ages past, the world of the Arcana and the human world were one. Their separation is a fact of history, cause unknown. Since then, the Ministry of Elemental Affairs has operated quietly in the background, maintaining the barrier between the two worlds — knowing that a second convergence would be catastrophic. The barrier is now under threat. Above Tokyo, a dimensional rift has opened and is growing. The young women called Maidens, who are the only humans capable of communicating with the Arcana, are also the only ones who can close it.