|“||No, no! I'm not all that popular at all, seriously.||”|
Oki has short, wavy black hair parted at the center-front, and blue eyes. He has a mole below his right eye. He wears a sun visor.
Oki is very obedient concerning objectives, vowing to snipe Chika with no mercy after Mizukami asks him to take care of her, thought during the actual match he says it'd make him feel bad and tries to make Ikoma take care of her instead. He becomes flustered when told that he is popular with girls and quickly denies that he is, but there are various rumors on whether he is popular or not. He seems to have a tendency to act in a flirtatious manner with girls. He has a good guy image, which annoys Ikoma, who believes it to be just an act.
Oki has an awkward relationship with Ikoma, who believes him to be popular with girls no matter how much Oki denies it, which leaves Oki really embarrassed. Ikoma is also annoyed by Oki's "good guy act". Nonetheless, they seem to be on good terms with each other.
Oki appears to like teasing Hosoi, as when she thinks to herself that Ikoma never called her cute, he quickly points out to the others, somehow knowing what she was thinking.
- (When Maori Hosoi is thinking to herself) "Mario-san's face says "He never said that about me before..."" 
- (When Ikoma calls him popular) "No, no! I'm not all that popular at all, seriously." 
- (About Chika) "I caught a glimpse of her just now. She moves with extreme care after firing every shot. She really is a good kid." 
- (About shooting Chika) "Ahhh~ I'm not actually that confident myself. This is such a sneaky tactic, a little girl like that. I'll definitely find it hard to shoot at her." 
- "Kōji" (孝二?) is composed of 孝 (filial piety, obedience, mourning?) and 二 (two?), while "Oki" (隠岐?) is composed of 隠 (hiding, concealment?) and 岐 (high, majestic, fork in road?).
- Like the rest of his teammates (with the exception of Minamisawa), he speaks in Kansai dialect.
- He likes akashiyaki, oden, cats, and shopping.
- "Okki", Ōji's nickname for Oki, is pronounced the same way as "occhi", the Italian for "eyes" (sing. "occhio"), which would explain the moniker and the icon.