Kouji Oki is a B-rank Sniper and a member of Ikoma Unit.

Oki is easygoing and confident. He has a tendency to act in a flirtatious manner with younger girls, complimenting them while saying that he would like them to be his sisters. He denies his popularity with girls and is very secretive about that aspect of his life. Nonetheless, he contested Touma's statement that he was slow to shoot at Chika in round six because she seemed to be going for a mutual hit, claiming that she was too cute for him to pull the trigger. This and similar protests are widely considered part of a "good guy" façade, and he is in fact willing to shoot, although it is possible that he finds sniping younger girls more distasteful than any other target.

(Source: World Trigger Wiki)