Rad in the Mai-Otome (manga) is a "Perfect Cyborg", one of the products of Schwarz's forbidden "Black Science", who retains only the nervous system and some internal organs after cybernetic enhancement. The manga does not explain why he underwent the conversion, as the Black Valley plague found in the anime does not exist in the manga. He does not know Yohko and in fact has absolutely no contact with her.
He first appears before the attack on the Artai embassy in Windbloom and is one of the attackers. A formidable warrior with his staff, he manages to cut an artillery piece in half with one strike and draw in battle against Shizuru even with the latter using her Robe.
When Manshiro and entourage arrive at the Black Valley, Rad is shown to be well-loved by its inhabitants and a role model of sorts that the children desire to emulate when they reach maturity.
Despite his earlier attempts on Manshiro's life, Rad eventually has a change of heart and protects the boy from the attacks of Akira while the boy is formally making his contract with Arika.
Rena identifies him as truly being Reito after reminiscing about his old persona and flashback panels are shown depicting Rena and Reito in earlier times, before she became an Otome and he a cyborg. Given that Rena should be over 40 years old by now, this Reito is the oldest of all the incarnations of him.
Reito does not survive to the end of the manga. In order to protect Manshiro from the attack of Cardair's Scale Sisters Otome trio, he lets himself get stabbed by them and self-destructs, presumably killing them at the same time. Before he dies, he beseeches Manshiro to be a good monarch and calls on Arika to be a star of hope. It is here that Arika gives in and finally acknowledges him to be her father.