Ryo is a young man of average height with blond hair and blue eyes who wears a beige trench coat, a light grey shirt, grey pants and brown shoes.
While never shown in the OVA's time frame, his form of Satan is nearly identical to his manga incarnation, having twelve golden wings and both a (covered) penis and breasts as they are intersex. Satan however, appears more feminine compared to the original manga, having full eyelashes.
Ryo is easily seen as the right hand of Akira Fudo, seeing each other as their best friends. As such Ryo assists Akira against the demons that invade the human world. This also extends to any enemy who stands against them including the cyborgs when they were thought to be a threat, shooting as 009 without mercy. Later he changes targets to Black Ghost's High Teen Cyborgs when they were directly involved in their affairs.
It is likely that Ryo held the same latent powers his manga incarnation had, but were not shown in the time frame of the OVA. However he still was incredibly athletic for his age in his human disguise. He was a crack shot with a gun he carried in his car. The gun resembles an assault rifle while featuring a drum magazine. Ryo is a proficient pilot, able to drive a modified car to pursue enemies and even drive a boat. He is also shown to be a brilliant computer hacker, as he was able to obtain data on Black Ghost by accessing their secret database from a dark net connection.
Ryo finds information about Demons attacking a nearby area and gets ready to assist Akira in battle. The night when Deviman battles and slays Pazuzu, Ryo intervenes when a cyborg appears. But the cyborg's immense speed keeps Ryo out of the main fight and only assists when both Cyborg 009 and Devilman are critically injured. With Akira reverting back to his human form, Ryo brings the injured Akira to his house but before leaving tells 009's companion 003 that demons aren't the only threat to them.
As Akira recovers, Ryo uses the dark net to hack into the files of Black Ghost after hearing their name from 003. The revelation causes some concerns, especially since an alliance has been formed between the parties. When Miki is kidnapped, Akira asks for Ryo's help in finding her. With information in tow, Ryo directs Akira to Dr. Adams' base. As Devilman battles the Cyborg Daemon, Ryo infiltrates the base while taking out a few guards with his gun. He finds Miki as well as Eva Maria Parallels/0015, who asks Ryo to get Miki to safety. After the battle, Ryo drives Akira and the unconscious Miki back home. With the battle over, Ryo is visited by the demon, Psycho Jenny who restores his original memories as Satan.