Ōyama (大山, Ōyama) is an ordinary boy who has no special talents. He is the third character to join the SSS. His roommate in the afterlife world is Hinata and he was the first character to be suspected to be an NPC. He has dark reddish hair and green eyes. He wears the afterlife school uniform in the manga. In the anime, he wears the standard SSS uniform. He does not excel at anything, but can do what any normal person can do. In other words, he is a jack-of-all-trades. He easily gets embarrassed in fake confessions. He has been in the afterlife world for longer than Hinata, and it is not known whether he is there from even before than Yuri.
At first he was thought by Hinata to be an NPC who he called "Villager A" which was inspired by NPCs in role-playing games; this assumption was dispelled when Hinata discovers that he knows that he is dead. Though he admits that he was once fearful of Yuri (because of what he did to Hinata), he helped Hinata in his relationship with Yuri.
an extended description!