Prince Subaru, son of Emperor Galfa, holds his royal position within the mechanical Galfa Empire. He shares the rare qualification to pilot the formidable Knight Gear Ogre, a distinction he holds alongside Arthea. Following the Spiral Castle's failed invasion of Earth, Subaru receives orders to locate the seventh Data Weapon, descending to the planet accompanied by Zero. His bond with Arthea runs deep, filled with profound affection and a brotherly regard. This intense connection ignites his hatred for Hokuto, the human pilot who usurps control of the Ogre, as Subaru perceives Hokuto stole Arthea from him.

While pursuing his mission on Earth, Subaru encounters Hokuto while the human pilot remains under the Galfa Empire's brainwashing. These interactions stir unfamiliar emotions within the prince—feelings of joy and loneliness that clash with his programming, causing internal turmoil and confusion. This marks a turning point, prompting Subaru to question his ingrained loyalties. As the conflict intensifies, Zero, viewing Subaru as expendable, attempts to betray and eliminate him. This act of treachery forces Subaru to critically reassess his place within the Galfa hierarchy.

Ultimately, Subaru joins the final assault against Emperor Galfa himself, aligning with GEAR and the Dendoh pilots to confront his father. His name, meaning "Pleiades" in Japanese, reflects the celestial theme common among key figures in the series.