Dreaming of a magical world every night, the young Toramizu Ginta yearns to be able to go there. With only his friend Koyuki believing in his dreams, Ginta remains positive despite the slander he receives from others over his dreams. But his wishes are answered, as one day a large door appears in front of Ginta, summoning him to the land of MAR Heaven. In this land, the weapons known as ARMS exist. While initially Ginta greatly enjoyed the discovery of this magical world, he soon learns of the terrible wars that have once plagued MAR Heaven and the upcoming war that may soon appear.
對異世界抱持憧憬的中學二年級學生虎水銀太被魔法召喚至異世界「MÄR Heaven」，在那個世界中存在一種稱為「ARM」的能夠賦予使用者力量的魔法物件。來到異世界的銀太和神奇的ARM巴波相會並先後結交到新的夥伴。肩負拯救MÄR Heaven世界的使命，銀太必須和夥伴們一起打敗邪惡的CHESS兵隊。