Nena Hargen is a supporting antagonist in the anime Agent Aika. She is a test tube baby created alongside or in a process similar to Rudolf Hagen, and it is uncertain whether she is his biological sister or simply a genetically engineered being with no blood relation. Regardless, she holds a deep and intense devotion to Rudolf, loving him to a degree that surpasses ordinary sibling affection. This attachment makes her jealous of Aika Sumeragi, whom she believes has seduced her brother.

Nena Hargen is characterized by a sadistic and unstable personality. She often walks around in minimal attire and takes pleasure in punishing the black Delmos under her command for any failures. Her role in the story is that of a loyal enforcer for Rudolf's plans, overseeing the Delmo corps and ensuring discipline. She directly opposes Aika and her allies, acting as a physical and tactical threat.

In terms of notable abilities, Nena Hargen receives from Rudolf a special Alternate Metal panty that allows her to transform into a powered-up form, enhancing her combat capacity. She is also depicted as a capable leader and fighter within Rudolf's organization. Her development across the series includes her deepening jealousy and eventual confrontation, with her fate intertwined with Rudolf's departure into space at the conclusion of the original OVA. She also reappears in the sequel AIKa Zero, continuing her antagonistic role.