The imaginary world Lingalind is enclosed by a mystical stretch of walls, seemingly shielding them from the unknown. Respected as the mother of the land, the wall regularly distributes celestial gift capsules titled "Rakuho" throughout the continent. The capsules show up once a month and contain metallic armbands that allow the wearer to transform into a cyborg called a "Briheight." The constant power struggles between the warring nations harshly impact Lingalind as each tries to take control of the Rakuho and strengthen their military capabilities. A Rakuho suddenly crashes in the countryside, carrying an unexpected visitor - a cryptic man with black hair. The entire population focuses on this unusual stranger, known as "Back Arrow," when he divulges that he hails from beyond the wall. Back Arrow's revelation creates chaos and a potential questioning of Lingalind's entire rigid principles.