Oniyuri serves in the Akane Class, a secluded all-female ninja village, as an upperclassman member of the Horse Squad. She has light gray hair reaching her waist, brown eyes, and stands 156 cm tall. Though the strongest combatant on her team, she does not lead it. Her personality is quiet, serious, and driven by a strong sense of justice; she supports morally correct actions and avoids underhanded methods, maintaining a logical and neutral perspective. She frequently assists other squads upon request.

Deep loyalty defines her bond with teammates Hinagiku and Kibushi. This loyalty was shown when she and Kibushi secretly prepared a birthday surprise for Hinagiku, causing a temporary misunderstanding where Hinagiku believed they were avoiding her. Oniyuri and Kibushi resolved this by intervening to protect Hinagiku from perceived exploitation. In another instance, Oniyuri joined Hinagiku's scheme to investigate the new student Rindou using deception and capture tactics, a plan ultimately thwarted by Tsubaki and Sazanka.

Her combat abilities surpass those of prominent fighters like Asagao and Sazanka. Her primary technique is the Shadow Possession Jutsu—also known as the Shadow Stepping Technique or Shadow Binding—which restrains opponents. Personally, she enjoys meat but dislikes vegetables. A recurring quote highlights her affection: "It’s fun to warm the Hinagiku cat with hands as warm as a hand warmer."