"Garoden" is a manga series set in a dystopian future where humanity is on the brink of extinction due to the emergence of monstrous creatures known as "Hollows." These beings, born from human despair and negative emotions, have overrun the world, forcing survivors to live in fortified cities. The story centers on a young man named Kaito, who becomes entangled in a secretive government project called "Garoden," designed to combat the Hollow threat. Kaito is chosen to pilot a biomechanical weapon known as an "Armor," a fusion of human and machine that grants immense power but at a great personal cost.

Kaito's journey begins when he loses his family to a Hollow attack, fueling his desire for revenge. As he trains to master the Armor, he discovers that the Garoden project is shrouded in dark secrets, including unethical experiments and the true nature of the Hollows. Alongside a group of fellow pilots, each with their own tragic pasts and motivations, Kaito battles both the external threat of the Hollows and the internal corruption within the Garoden organization. The narrative explores themes of sacrifice, identity, and the blurred line between humanity and monstrosity as Kaito and his comrades struggle to protect what remains of their world.

The series features a diverse cast of characters, including Rei, a stoic and skilled pilot with a mysterious connection to the Hollows; Aya, a compassionate medic who questions the morality of the Garoden project; and General Kuroda, the enigmatic leader of the operation, whose true intentions remain ambiguous. As the story progresses, alliances are tested, and the pilots must confront the possibility that their fight against the Hollows may be more complex and morally fraught than they initially believed. The plot builds toward a climactic confrontation that challenges the characters' resolve and forces them to reevaluate their purpose in a world teetering on the edge of collapse.