"Gad Guard" is set in a dystopian future where society is divided into the affluent Day Town and the impoverished Night Town. The story centers on Hajiki Sanada, a young delivery boy living in Night Town, whose life takes a dramatic turn when he encounters a mysterious object known as a Gad. This Gad transforms into a powerful mecha called a Techode, specifically the Lightning, which Hajiki pilots. The emergence of the Techode draws the attention of various factions, including criminals, corporations, and government agents, all seeking to control the power of these machines.

Hajiki is joined by a diverse group of characters, each with their own motivations and connections to the Techodes. Katana, a skilled fighter and rival, pilots the Shadow Techode, while Arashi, a mysterious girl with a tragic past, becomes entangled in the conflict. Other key figures include Takumi, a young inventor, and Catherine, a corporate agent with her own agenda. As Hajiki and his allies navigate the complexities of their world, they uncover the origins of the Gads and the Techodes, revealing a deeper conspiracy tied to humanity's survival.

The narrative explores themes of class disparity, technological advancement, and the ethical implications of power. The characters' interactions and personal growth are interwoven with intense mecha battles, as they confront both external threats and internal conflicts. The series balances action with character-driven storytelling, culminating in a resolution that addresses the fate of the Techodes and the future of their world. "Gad Guard" presents a cohesive and engaging tale, blending science fiction elements with human drama in a distinctive setting.