Rei Midoriyama, often referred to as Rei, is a central figure in the twenty-two-episode mecha series Super High Speed Galvion. At twenty-three years old, she is the heiress of the powerful Midoriyama financial conglomerate and also works as a special police investigator. After deducing that the secret organization Shadow is plotting global domination, she forms a private police team called Circus to oppose them. She recruits two convicts, Mu and Maya, by offering them reduced sentences in exchange for piloting the team's primary transforming mecha, the Galvion.

Rei’s background is marked by personal tragedy. Her father, Rob Midoriyama, is murdered by Shadow shortly after she establishes Circus, and she is forced to take control of the family business while continuing her fight against the conspiracy. Despite her privileged upbringing, Rei has a straightforward, no-nonsense personality. She is described as attractive and charismatic, but also levelheaded and effective at directing her subordinates. She does not pilot the Galvion herself; instead, she acts as the strategist and commander of the Circus team, providing intelligence, resources, and overall leadership.

Her primary motivation is justice, driven by the loss of her father and a desire to stop Shadow’s influence over world governments. She is pragmatic and willing to use unconventional assets, such as convicted criminals, to achieve her goals. Later in the series, she becomes the object of affection for the antagonist Henry McMillan, a charismatic Shadow executive who pursues her aggressively. Rei rejects his advances, maintaining her focus on her mission.

Key relationships include her bonds with the Circus members, particularly Mu and Maya, whom she trusts to carry out dangerous missions. She also has a loyal android bodyguard named Inka. The planned continuation of the series would have seen Rei kidnapped by Henry, further developing the conflict between them. In terms of abilities, Rei is a capable investigator and administrator, wielding her wealth and influence as weapons. She is not shown as a frontline fighter, but her strategic acumen and determination make her indispensable to the Circus team. Over the course of the broadcast episodes, she grows from a wealthy heiress into a hardened leader, bearing the weight of her father’s legacy and the ongoing battle against Shadow.