Every night, Toramizu Ginta dreams of a wondrous world and yearns to enter it. Despite being ridiculed by others for his beliefs, Ginta perseveres with the support of his friend Koyuki. One day, a colossal door appears before him and transports him to the land of MAR Heaven where ARMS, mystical weapons, exist. Though enchanted by the new world, Ginta discovers the horrors of past battles and the looming threat of a new war.