Rumi Usagiyama, the Pro Hero known as Mirko, holds a high rank among heroes. She possesses an athletic build with pronounced musculature, tan skin, red eyes, and long white hair. Her Rabbit Quirk manifests in the form of long white rabbit ears and a small, round white tail. Her hero costume is a sleeveless white leotard with dark purple trim at the shoulders and waist, featuring a wide yellow crescent moon on the chest. A single thick metal plate wraps around her midriff. She wears purple thigh-high boots armored at the heels and toes to resemble rabbit feet, along with thick white gloves featuring long cuffs. She sustained critical injuries during the raid on Jaku General Hospital, including a crushed left forearm, a stabbed right shin, and the tip of her right ear being sliced off. These injuries resulted in her receiving a prosthetic left forearm and a prosthetic right leg, both of which are interchangeable. In the Final War, her right forearm was bitten off, requiring further prosthetic replacements. After the hospital raid, she cut her hair to just below her jaw and acquired several scars. Rumi Usagiyama is tough, outspoken, and confrontational. She respects forthright individuals and criticizes heroes who join teams, viewing them as potentially reliant on others rather than their own strength. She operates fearlessly and independently, without an agency or sidekicks, and enthusiastically confronts life-threatening situations. She lives without regrets and is willing to sacrifice her life for the greater good. She exhibits a high pain tolerance and remains pragmatic in combat, demonstrated when she used her own hair as a tourniquet after losing a limb. While she prefers to work alone, she is capable of assisting and requesting help from other heroes during major crises. In her youth, she was a legendary schoolgirl hooligan in Hiroshima, often crashing fight clubs and earning the nickname "bunny-eared Usako," which led to her expulsion from middle school. She later attended a hero school in Hiroshima. During a school trip to Osaka, she infiltrated the illegal Underground Masquerade fighting event under the alias "Masked Mystery Beauty: Tiger Bunny." There, she encountered All For One and was rescued by the Pro Hero O'Clock after an attempt was made to steal her Quirk. She assisted in managing the crisis, which concluded with All Might's intervention, and she declined any compensation, stating her intention to succeed on her own merits. As a Pro Hero, she achieved the rank of No. 5, becoming the highest-ranking female hero in Japan. She publicly criticized team-based hero work at the Japanese Billboard Chart JP event. She later assisted Endeavor and Hawks against Dabi after seeing their battle on a news broadcast. During the Paranormal Liberation War, she participated in the raid on Jaku General Hospital. She breached Dr. Kyudai Garaki's laboratory, destroyed numerous Nomu tanks, and engaged multiple High-End Nomus. Despite severe injuries, including the loss of her left arm and damage to her right leg, she destroyed Tomura Shigaraki's incubation capsule before being rescued. In the Final War, she fought Tomura Shigaraki on the floating U.A. arena alongside other heroes, during which she lost her right forearm but continued fighting. Eight years later, she remained a Pro Hero, ranked No. 6, with updated prosthetics and longer hair. Her Rabbit Quirk grants her the physical attributes and abilities of a rabbit, including enhanced leg strength for powerful jumps and kicks capable of shattering concrete and creating shockwaves. She also possesses enhanced hearing, smell, and sharp animal instincts for detecting danger. Her fighting style specializes in a variety of kicking techniques. Her named techniques include Luna Ring, a cartwheel kick for multiple targets; Luna Fall, a powerful downward kick; Luna Tijeras, a decapitating move using her legs; Luna Arc, a front-facing axe kick; and Luna Rush, a series of high-speed kicks. Following her injuries, she employs advanced prosthetic limbs. Her initial prosthetic left arm could fire a large laser, and her post-Final War upgrades included multi-barrel guns and rapid-fire capabilities. She has parents and extended relatives with whom she maintains a good relationship; her parents visit her regularly. She is the only Pro Hero on her father's side of the family, though her maternal great-grandmother was also a hero. Not all family members possess the Rabbit Quirk; some have mixed variations. She has consistently expressed a dislike for team-based hero work but has participated in coordinated efforts during major crises like the Jaku Hospital raid and the Final War. She has also collaborated with U.A. students on spin-off missions.