Imagine you're a regular high school student, and one day a powerful, talking mechanical arm suddenly attaches itself to your body. That’s the reality for Hikaru Amatsuga. This bizarre new limb is Alma, a "Mecha-Ude"—a sentient, mechanical lifeform of immense power. The shy Hikaru and the wisecracking Alma must learn to cooperate, a difficult task when they can’t even agree on what to do next.
Soon, they are discovered by ARMS, a resistance group that protects Mecha-Ude from corporate hunters and rival users. Hikaru and Alma join forces with other human-Mecha-Ude pairs, engaging in spectacular, high-speed battles across the city of Tokyo. The series has ended, but sign up for a reminder just in case it returns.