"Promare: Lio-hen" is a spin-off film that expands on the events of the original "Promare" movie, focusing on the character Lio Fotia and his journey. The narrative delves into Lio's backstory, exploring his role as the leader of the Burnish, a group of individuals who possess pyrokinetic abilities due to a mysterious phenomenon called the Burnish Flare. The Burnish are persecuted by the authoritarian government of Promepolis, which views them as a threat to society. Lio and his faction, Mad Burnish, fight against this oppression, seeking to protect their kind and uncover the truth behind their powers.

The story begins with Lio and his comrades engaging in acts of rebellion against the Freeze Force, a military unit tasked with suppressing the Burnish. Lio's resolve is tested as he faces the moral complexities of his actions, balancing his desire for justice with the potential consequences of his fiery abilities. The narrative also introduces Galo Thymos, a member of the Burning Rescue firefighting team, who initially opposes Lio but later becomes a key ally. Their dynamic shifts as they uncover shared goals and mutual respect, leading to a pivotal alliance against a greater threat.

As the plot unfolds, Lio discovers the origins of the Burnish Flare, which is tied to a larger conspiracy involving the Promepolis government and a powerful entity known as Kray Foresight. The revelation forces Lio to confront the true nature of his powers and the sacrifices required to protect both the Burnish and humanity. The film culminates in a climactic battle where Lio, alongside Galo and their allies, must challenge the forces seeking to exploit the Burnish for their own gain.

The narrative emphasizes themes of resistance, identity, and the struggle for equality, with Lio serving as a symbol of defiance against systemic oppression. His character arc highlights his growth from a determined rebel to a leader willing to bridge divides for the sake of a better future. The film enriches the "Promare" universe by providing deeper insight into Lio's motivations and the broader conflict between the Burnish and Promepolis, offering a compelling exploration of its central themes and characters.