Returning to school in the evening to grab a forgotten lunch box appeared to be an ill-advised decision for Mangetsu Kohinata. Upon arriving, she unexpectedly finds herself transported to a bizarre realm where powerful magical warriors clad in massive armor engage in an intense battle. Despite the unfavorable circumstances, Mangetsu's entrance into this unfamiliar world was not a blunder, as she emerges as a mage with the ability to summon and manipulate her own massive armor. Together with her enigmatic newfound companion Shingetsu, Mangetsu must hone her skills to compete against other mages for the unbelievable reward of regulating the lost magic that once governed our planet.