Nina Tucker is the young daughter of Shou Tucker, a State Alchemist known as the Sewing-Life Alchemist. She lives with her father and their large pet dog, Alexander, in a house in an eastern border city. At around five years old in the manga and the Brotherhood adaptation, she displays the cheerful, playful, and trusting nature typical of a child her age, often seen playing with or embracing Alexander. She loves her father deeply and maintains a steadfast faith in him, unaware of the darkness within his work. Her mother is absent, and Nina tells the Elric brothers that she left the family, though the truth is that her mother was used as a human test subject in Shou Tucker's chimera experiments and died.

Nina's primary motivation is to be loved and to make her father happy. She craves attention and companionship, which is why she quickly bonds with Edward and Alphonse Elric when they arrive to study bio-alchemy under her father. She refers to both brothers as "big brother" and delights in playing with them and Alexander. Her innocent desire to help her father retain his State Alchemist certification leads her to reassure him that she and Alexander will make sure he does not lose his license, unwittingly inspiring him to resort to his most depraved act.

In the story, Nina serves as a tragic catalyst. Her role is short-lived but emotionally devastating. After Shou Tucker’s annual assessment puts his position at risk, he transmutes Nina and Alexander into a speaking chimera, fusing them into a single dog-like creature. The Elrics discover the truth when the chimera speaks Nina’s voice and calls out to Edward, and they are horrified by their inability to reverse the transmutation. Nina, even in her monstrous form, pleads for her father’s life when Edward attacks him. Soon after, the serial killer known as Scar arrives, kills Shou Tucker, and then ends Nina’s life as an act of mercy, believing her existence as a chimera to be a torment.

Nina’s key relationships are defined by betrayal and care. Her father, whom she adored, sacrifices her for his career. Alexander, her beloved pet, becomes part of her being. Edward and Alphonse become temporary older brother figures; they play with her, sympathize with her loneliness, and fail to protect her, which leaves them with lasting guilt. Her development is minimal as a character, but her transformation and death profoundly affect the Elrics’ emotional growth and their understanding of the limits of alchemy and the cost of human ambition. She has no inherent alchemical abilities, but as a chimera she retains the power of human speech. Her legacy is one of heartbreak: she haunts Edward’s dreams and becomes a constant reminder for both brothers of the evils that can arise when alchemy is used without moral restraint. In the final confrontation with Truth, Edward even cites his failure to save a little girl as proof of his humanity. Nina Tucker’s story underscores the series’ themes of family, sacrifice, and the consequences of unchecked scientific pursuit.