"Go Dannar" is a science fiction mecha anime set in a post-apocalyptic world where humanity faces constant threats from biomechanical creatures known as "Orochi." The story unfolds in a future where Earth's environment has been devastated, and remnants of human civilization survive in isolated city-states. To combat the Orochi, humanity develops massive humanoid robots called "Dannar," piloted by skilled warriors.

The protagonist, Ryo Magami, is a young and determined pilot who operates the Dannar unit "Dannar Base." Ryo is driven by a personal vendetta against the Orochi, as they were responsible for the death of his parents. Alongside him is Miu, a mysterious girl with a deep connection to the Orochi, who becomes a key figure in the battle against the biomechanical menace. Miu's origins and her unique abilities are gradually revealed as the story progresses, adding layers of intrigue to the narrative.

The series explores the dynamics of teamwork and survival as Ryo and Miu join forces with other pilots and factions to protect humanity. The Dannar units are not just weapons but also symbols of hope and resilience. The plot delves into the ethical dilemmas of using advanced technology to fight the Orochi, as well as the consequences of humanity's past actions that led to the current state of the world.

As the conflict intensifies, Ryo and his allies uncover deeper secrets about the Orochi and their connection to Earth's history. The story balances action-packed mecha battles with moments of character development, particularly focusing on Ryo's growth as a leader and Miu's struggle with her identity. The narrative builds toward a climactic confrontation that tests the limits of human ingenuity and determination in the face of overwhelming odds.