She is a fusion of a rat and a cat, but this setting is not highlighted much because she is only called by the nickname 'Mouse' both inside and outside the work. She is a white rat with short blonde hair wearing a nurse's outfit. She is 23 years old. According to a past Bilibili video by Gutian re-uploaded by a fan, Rona was a normal white rat in the past. After witnessing other rats being experimented on in a laboratory, she was traumatized when her own organs were removed, leaving her with an empty body that was thrown into a waste bin. The process of how she became the current rat beastman is still unknown. Because she was experimented on by humans in the past, she is favorable toward other small animals but extremely loathes humans. It is said that she started working at the hospital after hearing the story of Mimi, a blue cat who also came to the hospital out of hatred for humans. No matter how psychopathic she is, she naturally does not kill the person who helped her. Her personality is infinitely kind to organization members and small animals; because of this, small animals trust and are friendly toward Rona, often helping her when she is in crisis. Also, in the arena, which effectively serves as a public execution ground, Rona helps beat children to death and enjoys it. However, she becomes extremely cruel toward humans outside the organization. She takes on the role of luring patients, mainly young children, with her cute appearance and then reveals a personality that combines psychopathy and sociopathy by inflicting cruel retaliation on them. It was later revealed in Episode 4 that adult humans are no exception. She has considerable physical endurance, easily withstanding a straight punch from Luke, who was doped with drugs. Ironically, considering Luke is a child, her combat ability is clearly good, but exactly how strong she is remains unknown. However, since she possesses drugs that enhance physical abilities, her own combat skills and resourcefulness seem outstanding. Nevertheless, she struggles somewhat against opponents with special abilities; for example, she is immediately suppressed by Dam and Bishi.