Rei Hijikata serves as the third battle racer trained by Professor Oogami and holds the distinction of being the sole female member within the Oogami Corps. This affiliation positions Rei directly against protagonists such as the Seiba brothers. Functioning as an antagonist, Rei pilots the specialized battle machine Ray Stinger, engineered for destruction rather than standard racing.

Rei demonstrates ruthless commitment to Oogami's philosophy early on by deliberately destroying Gou Seiba's Victory Magnum beyond repair. This aggressive tactic, targeting opponents' machines, defines Rei's initial narrative role.

Significant development occurs during the Japan Cup arc. Rei executes a pivotal "Heroic Sacrifice," destroying Ray Stinger to shield J's Proto-Saber Evolution from Gen Kondo's Brocken Gigant. This protective act marks a decisive break from prior antagonistic methods, rejecting battle racing in favor of the series' emphasis on sportsmanship.

Visually, Rei possesses blue hair and brown eyes and a feminine appearance, though the narrative does not depict in-universe characters mistaking Rei for a girl. This design contrasts with Rei's initially combative demeanor.