Akira Natsume, a regular teenager with an intense fear of electronics, aspires to emulate his successful older brother Shuuichi's accomplishments. However, his life takes a drastic turn when he is struck by a truck while saving a girl from troublemakers. Awakening to a shocking reality, Akira finds himself trapped inside an advanced weapon known as an EX-ARM, 16 years post-accident. Guided by Minami Uezono, a police officer, and aided by the android Alma, Akira must navigate a world where his brain controls a powerful weapon capable of great devastation. As Akira adapts to his new existence, he joins forces with the EX-ARM Countermeasure Division to combat crimes perpetrated by similar machines, all the while unraveling the mysteries surrounding his transformation.