Nia is a young female DearS, a member of the alien race that has integrated into human society. She is a "Biter" DearS in training, a role that functions similarly to a police authority within DearS culture, and she serves as an apprentice to the more senior DearS named Xaki. Her primary assignment is to capture Ren, a defective DearS who has bonded with the human protagonist Takeya Ikuhara. However, Nia frequently forgets or fails in this mission due to her scattered and easily distracted nature.

She has a bright and cheerful personality and is considered the most outgoing among the DearS. She is energetic, friendly, and quick to make friends, often approaching others with an open and enthusiastic manner. Her speech is marked by her trademark nonsense syllable "nii," which she adds to the end of her sentences, giving her a playful and childlike quality. Despite her amiable demeanor, she also possesses a surprising level of physical agility and is capable in combat when the situation demands it.

Nia's motivations shift over the course of the story. Initially, she is focused on advancing to become a full-fledged Biter by capturing Ren, but her priorities change after she meets Takeya. She develops a strong fondness for him, referring to him as "Onee-chan" and treating him like an older brother. She appreciates his kindness when he gives her food, and she tells him that if she were to remain a sheep, she would want him to be her master. Because of this bond, she eventually abandons her mission to capture Ren, showing that her loyalty to her new friends outweighs her original orders.

Her key relationships include her mentor Xaki and Takeya, who becomes a central figure in her life. She also befriends Takeya's younger sister Natsuki, and she becomes a welcome presence in their household. In the manga, when Ren is kidnapped, Nia actively helps Takeya venture inside the DearS ship to rescue her, demonstrating her bravery and dedication to those she cares about.

Throughout the series, Nia shows growth from a forgetful apprentice into a more reliable and compassionate figure. Her experiences with humans help her mature, and she learns to navigate the complexities of relationships and the challenges of being a DearS on Earth. She remains a consistently affectionate character, bringing warmth to the story through her interactions. In terms of abilities, she is physically strong and agile, especially in combat, and she is quick on her feet when needed, despite her usual clumsiness. Her catlike appearance, with green eyes and bright orange hair styled in two pigtails, contributes to her distinctive design.