Nadja Applefield is the central protagonist of the anime Ashita no Nadja. She is a Franco-Austrian girl who grew up at the Applefield Orphanage in early twentieth-century England, having been left there as an infant with only an elaborate heart-shaped brooch as a possession. She spent her childhood believing her parents were dead, but shortly before her thirteenth birthday, she received a mysterious package in the mail containing a ball gown and a diary that had belonged to her birth mother, along with a letter suggesting her mother might still be alive. This revelation sparked her desire to find her mother and set the course of her journey.

In terms of personality, Nadja is described as sunny, charming, and naturally sociable, with a talent for making friends wherever she goes. She carries responsibility well, having often helped care for the younger children at the orphanage. However, she is also impulsive to the point of foolhardiness and extremely trusting, which sometimes leaves her vulnerable to being taken advantage of or manipulated by others. Her primary motivation throughout the story is her dream of being reunited with her mother.

Nadja's role in the story begins when two men arrive at the orphanage to steal her brooch, and a fire breaks out, forcing her to leave. She joins the traveling Dandelion Troupe as a dancer, using the troupe's itinerant lifestyle to search for her mother while also developing her performing talents. As the main character, she travels across Europe, meeting many friends and facing numerous challenges, all while learning the truth about her parentage and discovering her own destiny.

Key relationships include her bond with the members of the Dandelion Troupe, who become a surrogate family, as well as her connections with the Harcourt twins, Francis and Keith. Early on, she feels attached to Francis and once mistakes Keith for him. As the series progresses, she develops romantic feelings for Keith, though she remains confused about her emotions. She is ultimately forced to choose between the two brothers near the end of the series. She first chooses Francis because she believes he was the first person to help her, though it was actually Keith. Francis later helps her realize she truly loves Keith, but in the end, she does not choose either brother and instead re-joins the Dandelion Troupe, with the implication that she will make a decision later.

Throughout the series, Nadja undergoes significant development. She grows from a sheltered orphan into a more independent and determined young woman, learning to navigate betrayal, confront impostors such as Rosemary who attempt to steal her identity, and assert her own path. Her notable abilities include a natural talent for dancing and singing, which become central to her role in the troupe, as well as a remarkable capacity for forming friendships and inspiring others with her hopeful and persevering nature. She maintains a firm belief that better days will come after difficult times, and thanks to her travels and experiences, she ultimately discovers a deeper understanding of herself and the meaning of family.