Nia is a mysterious young girl found sleeping in a capsule in the middle of a dump site by Simon when he was still distraught over Kamina's death. Later revealed to be Lord Genome's daughter, she learns the harsh reason why her father left her to die. She had no prior contact with humans except her father, though she is very curious, pure and innocent. Despite early misgivings from her lineage, she is quickly accepted by Team Dai-Gurren, much to the initial irking of Yoko, who later becomes a close friend of hers. During her journey, she develops a strong empathy for Simon and joins him in the final confrontation against her father.
Seven years after the war with the Beastmen, Nia receives a marriage proposal from Simon. She refuses at first, after her bubbly contrived logic causes her to misunderstand his words, but after receiving counseling from Kiyoh and Kiyal, she decides to accept. However, when the population limit is reached, the Anti-Spiral data awakens within her and permanently converts her into an Anti-Spiral virtual lifeform, serving as the Anti Spirals' emissary in charge of Earth's Human Extermination System. But in spite of her emotionless persona and being a step ahead of Team Dai-Gurren, Simon points out to Nia that all her actions and appearances before him were in fact the act of her true feelings of her former self, who urges Simon to keep fighting, allowing Nia to have the strength to return to her former self while ending the Human Extermination. However, she is transported back to the Anti-Spiral homeworld so the data on Team Dai Gurren can be extracted from her for analysis, with Simon vowing to rescue her. Although she is saved, the Anti-Spiral's death makes Nia fade away because her existence as a program is dependent on the Anti-Spiral Race. She lasts long enough to be wed to Simon before vanishing, leaving behind only her ring. In the epilogue, which takes place 20 years later, a memorial site is seen in her honor, located right next to Kamina's burial ground.