Nana is a young Diclonius known as Number Seven or Silpelit number seven. Unlike most Diclonius infants, she was not euthanized at birth but was kept alive and subjected to experiments at the Diclonius Research Institute. She has the appearance of a young teenager about twelve to fourteen years old, but due to the accelerated aging of Silpelits, her actual age is roughly six years old. Her name, Nana, is the Japanese word for the number seven, the designation she was given in the facility.

Her background is defined by the unusual kindness she received from Kurama, the chief researcher at the institute. Kurama treated her as a surrogate daughter, and she came to call him Papa in return. Under his guidance, she learned that her telekinetic vectors should never be used to harm humans. This nurturing relationship gave Nana a fundamentally gentle and empathetic personality, making her a stark contrast to other Diclonius who often become violent due to mistreatment.

Nana's primary motivation is to earn Kurama's approval and to protect those she cares about. This desire drives her to take risks, such as when Kurama sent her to locate the escaped Diclonius Lucy. Rather than merely tracking Lucy and waiting for backup, Nana attempted to capture Lucy herself in hopes of impressing Kurama. The confrontation ended disastrously: Lucy viciously dismembered Nana, tearing off all her limbs. Kurama intervened and saved her life, defying orders to euthanize her. He provided her with artificial limbs that she can control using her vectors, along with a large sum of money, and set her free.

Cast out into the world with little understanding of human society, Nana initially struggled. She burned some of the money for warmth, not realizing its value, until she met the young runaway Mayu, who taught her about everyday life. Following her recovery, Nana eventually faced Lucy again, this time encountering Lucy's childlike alternate personality Nyu.

Nana's personality is friendly, kind, and compassionate, though she occasionally enters trance‑like states where she becomes cold and serious, reminiscent of Lucy's default demeanor. She is driven by a strong desire to be useful and to protect others, often placing their needs above her own. Despite her gentle nature, she possesses notable abilities. She can manifest four invisible telekinetic vectors that extend up to three meters, giving her greater range than Lucy. She can use these vectors to manipulate objects, control her prosthetic limbs, and even throw those limbs like projectiles. A unique skill is her ability to temporarily disable the vectors of other Diclonius by directing her vectors through their pineal glands. However, her lack of killer instinct and her empathy limit her combat effectiveness; she lacks Lucy's raw strength and willingness to inflict harm.

Her role in the story is to serve as a moral counterpoint to Lucy and to demonstrate that Diclonius are not inherently homicidal. Nana's development traces her journey from a lab subject entirely dependent on Kurama to an independent individual who learns to navigate human society and form bonds with others. She becomes part of the small group surrounding Kouta and Yuka, and her presence highlights the theme that environment and compassion can shape a Diclonius's nature. Her key relationships include her deep father‑figure bond with Kurama, her conflicted rivalry with Lucy, and her friendship with Mayu, who helps her adjust to the outside world.