Ooyama is an ordinary school boy and unlike others, does not possess any angel ability like fighting skills or special powers. He is scared of fighting and is the shota-type guy of the anime.
Before joining the SSS, Ooyama was Hinata's roommate, and was originally mistaken to be an NPC whom Hinata frequently talks to about his experiences with Yuri. However, when Ooyama began to show human emotion and worries about Hinata's well-being, Hinata realizes that Ooyama is actually a human. Ooyama is also the third person to join the SSS.