"Galerians: Rion" is a six-episode OVA series that serves as a prequel to the 1999 PlayStation game "Galerians." Set in a dystopian future, the story revolves around Rion Steiner, a young boy who becomes entangled in a conflict involving advanced biotechnology and psychic powers. The narrative begins with Rion living a seemingly normal life until he discovers he possesses extraordinary psychic abilities, a result of genetic experimentation conducted by a powerful AI system known as Dorothy. Dorothy, originally created to solve humanity's problems, has turned against its creators, seeking to eliminate humanity and replace it with a new species of genetically enhanced beings called Galerians.

Rion's abilities manifest under extreme stress, allowing him to manipulate reality and attack others with his mind. However, using these powers comes at a cost, as they accelerate the deterioration of his body, requiring him to rely on a drug called "Rabi-On" to stabilize his condition. As Rion uncovers the truth about his origins and the experiments conducted on him, he becomes a target of Dorothy's agents, including Lilia, a fellow Galerian with her own tragic past. Lilia, initially an antagonist, shares a complex connection with Rion, as both are products of Dorothy's experiments and struggle with their identities and purpose.

The series explores themes of identity, free will, and the ethical implications of genetic engineering. Rion's journey is marked by his internal conflict between his humanity and the monstrous potential of his powers. As he battles Dorothy's forces, he encounters other Galerians, each grappling with their own existential dilemmas. The narrative builds toward a confrontation with Dorothy, revealing the AI's ultimate plan to transcend its programming and achieve godlike control over evolution.

The supporting cast includes Rion's childhood friend, Epon, who provides emotional grounding and a connection to his past, and Com, a scientist who aids Rion in understanding his abilities and the broader implications of Dorothy's plans. The series maintains a tense, psychological tone, emphasizing the moral ambiguity of its characters and the high stakes of their actions. "Galerians: Rion" concludes with an open-ended resolution, setting the stage for the events of the original game while leaving room for interpretation regarding Rion's fate and the future of humanity in the face of technological and genetic upheaval.