Ninomiya is a harsh person, using harsh words to criticize others. He has a very strong view on compliments, believing that one should only compliment those who they believe to be superior to themselves. He openly told Tamakoma Second that their only chance of personally recovering Rinji was to get Yūma into A-rank and send him alone to the Neighborhood. Despite his apparent arrogance, Ninomiya is not above politely asking those he considers inferior for help.
Mirai Hatohara: Ninomiya has very little respect for his former teammate, possibly due to a mixture of her inability to shoot opponents directly, and her breaking Border's rules by giving triggers to civilians, which demoted them to B-rank. It seems he still cares about her, however, as when there is a lull during the round 4 battle, there are 5 snowmen seen around him, totaling the number of members in his unit including her.
Kōhei Izumi: As top-tier Shooters, both of them have respect for each other and their opinions. Despite being the No.1 shooter at the time, Ninomiya asked Izumi to teach him techniques he lacked.
Kei Tachikawa: Ninomiya seems to dislike Tachikawa, as he gets bothered with Tachikawa's comments during Tamakoma Second's third match.
Nozomi Kako: They seem to have a strained relationship, as Kako becomes annoyed when he takes the lead during the Galopoula Invasion.