Nemu serves as lieutenant of the 12th Division under Captain Mayuri Kurotsuchi. She's an artificial being—literally created by Mayuri as a blend of his research into artificial bodies and souls—which explains her quiet, withdrawn demeanor around him. Their dynamic is anything but typical; Mayuri treats her less like a daughter and more like an expendable tool, regularly throwing her into danger as bait. About the only credit you can give him is that he occasionally admits to taking pride in his work—meaning pride in creating her, not in her as a person. Nemu's been through a lot at his hands, yet she remains fiercely loyal to him anyway, even worrying about his safety. Fans often note this seems rooted in gratitude that he gave her existence in the first place. Where she differs from Mayuri is in her capacity for actual compassion; she once saved Uryū Ishida's life simply as thanks for him sparing her father.
In combat, her style blends capoeira-influenced martial arts with kidō. More notably, her body was engineered to take serious punishment—she can survive injuries that would kill normal people, though she still feels the pain. This durability extends to withstanding some truly horrific things, like being used as an incubation vessel by Szayel Aporro Granz. Mayuri can rebuild her quickly afterward, letting her get back to work. She's also immune to Mayuri's arsenal of poisons, which is convenient since she carries around antidotes and her own collection of toxins and potions derived from his research—making her genuinely dangerous if someone tries to attack her from the inside. While she doesn't normally carry a zanpakutō, an artbook illustration confirms she has one: a thin katana.
Content compiled by AnimeList.moe from publicly available sources.