Rei Ozora first appears in Episode 21 of the first season and Episode 33 of the second season. Significantly younger than his peers, his high intelligence allowed him to assist in designing and constructing his own unit, the Shinkalion 800 Tsubame. This unit was the first capable of flight, utilizing a Double Wing System with large Swallow Wings on its back for gliding and smaller Sub Wings on its legs for aerial adjustment. It was also armed with a Pantograph Arrow weapon that fires energized bolts for ranged combat.

Despite his intellect, Rei exhibits the eagerness and naivety of a child. He initially operated without fear until a reckless action during the Second Underground World Strategy placed him in grave danger, an event which became a significant point in his personal development. He holds deep admiration for the senior drivers from the Ōmiya branch, having researched them prior to their meeting. He quickly idolized the trio of Hayato Hayasugi, Akita Oga, and Tsuranuki Daimonyama for their experience, referring to them as his masters.

After the conflicts with the Kitoralsus ended, Rei resigned as a driver and was transferred to the Sakurajima Testline facility as an engineer. His original Shinkalion, the 800, remained on standby until it was refitted into the Z 800 version by Yokokawa Branch engineers. This transition from driver to engineer marks a maturation in his character, though he retains his excitement and admiration for his original idols, readily reverting to his eager self upon learning of Hayato Hayasugi's return to Japan.

His relationships within the Shinkansen Ultra Evolution Institute include former superior Akatsuki Ogura, former teammates Gin Itsutsubashi, Jō Itsutsubashi, and Takatora Kirishima, current colleagues Nagato Yamaguchi and Kintoki Odawara at Sakurajima Testline, and current superior Futaba Mihara.