As a child, Nagi's parents were part of the scientists that worked with the aliens known as the visitors to create the organization known as TLT. It is assumed she spent some part of her childhood in Colorado. Around that time the being known as Dark Zagi came to Earth took the body of one of the researchers as his host. The evil Ultra murdered the entire team present at the time, dropping the body of her mother in front of a young Nagi as she searched for her mother in the woods. Although Nagi's memories of that event were somewhat clouded, most likely due to Zagi's powers but the impact of it left her scarred for the rest of her life and a deep hatred of anything inhuman, especially those that took on human form.
Years later, she would join the same organization her parents worked to create, TLT, as a Night Raider for the goal of wiping out any and every space beast for the sake of revenge. As a rookie she was under the tutelege of the then Deputy Captain Mizorogi Shinya, whom she grew to admire deeply and have feelings for. The two grew a deep bond wherein they confided with each their deepest fears and secrets.
One night he and Nagi went into a building alone and found themselves facing the zombie variant of Beast Humans, corpses animated by beast cells and manipulated by some dark power as puppets. After dealing with them the two decided that only one would face the beast, its ability made working in a team liability. He and Nagi made a pact to kill the other if they fell under the creature's power, switching dog tags to seal their promise. However, Mizorogi was never seen afterwards, as far as she and the others knew he was dead.
As time passed with Komon's recruitment into the Night Raiders and Jun Himeya taking up the mantle of Ultraman, the now Mephisto possessed Shinya appeared and battle with the Night Raiders several times and was proven a powerful foe. Shinya later called to Nagi to fullfill their promise to each other and appearantly would have swayed her to his side had Himeya, Wakura and Komon not appeared. The appearance of Shinya's dark field and Galberos made him seem unstoppable until Nagi shot her old lover in the back, causing him to retreat and proving that she never had any desire to join him. Nagi later participates in Ultraman's final battle with Mephisto which ended with both being presumed KIA.
Some time after the light picked Ren as the new Deunamist, Nagi was made aware of an amnesiac Shinya unaware of his past. When Shinya escaped custody, after regaining his memories, Nagi and Komon went after him and his hostage. Despite their desire for vengeance, it seemed the situation would've ended peacefully had Shinya not been shot by Misawa. When Misawa revealed himself to be the next Dark Giant, he attacked and forced the three into retreat. Fleeing from the giant, Komon and Nagi watched on as Ren, as Ultraman, appeared to fight him in what would be a losing battle. However, as the villain prepared to finish off the giant of light, Mizorogi called upon his power, taking the form of a Dark Ultra again, this time, however, he had complete control of himself. He was no longer a puppet and now used this destructive force for good. Saving Ultraman, the two Mephistos clashed in a show of power, but Shinya's wounds slowed him down. Zwei stabbed his blades into Mephisto’s gut, the former dark giant was about to fall. Yelling for Ultraman to fire as he spun around and held the other tight, knowing he had reached the end of this power and life. Ren fired his Arrow-Ray Schtrom, killing Dark Mephisto Zwei while Mizorogi reverted to his human form where he would die, once and for all, as a human whom had redeemed his soul in Nagi's arms. Before his end, he told Nagi of the being known as Unknown Hand, who had controlled him all along, the space beasts and the other dark giants. He also told her that he was someone inside TLT and close to them.
After Ren's final battle with Izmael, Nagi inherited the light with the Evolthruster appearing in her hand in the middle of the base as she walked down a hallway. Unknown Hand sensed the light within Nagi, and finally revealed himself as Night Raider analyst, Mitsuhiko Ishibori. Turning on the others he seemingly killed Shiori, wounded captain Wakura and nearly killed Komon if not for Nagi's timely arrival. Despite her new powers Nagi could do little to stop his march to Level O as he reflected her attack back at her and left.
Ishibori then entered Level 0 of the base and breached the security field put up by the visitors. Their potential barrier and therefore their powers where weakened thanks the recent appearances of Space Beasts in populated areas. With them out fo the way he was free to gain access to Lethe. Eventually Illustrator (in the flesh), Komon, the captain and Nagi all arrived to halt his progress. It was then that he revealed his true name, Dark Zagi. He then easily defeating all resistance against him, as Zagi revealed the depths of his machinations, he spoke of how he knew Nagi would one day be a Deunamist and so everything he did, creating Faust and Mephisto was done to strengthen the light for when she acquired it.
Zagi taunted Nagi, revealing himself as the one who had murdered her parents many years ago. This was all done to get her to act from her own hate filled impulses and transform into Ultraman. Despite Illustrator's protests Nagi transformed, succeeding in nothing more than allowing his plan to succeed. Nagi's hatred acted as a catalyst to stir Lethe's programming of holding all memories connected to space beasts. The construct unleashed tendrils of darkness that bound Nexus to Lethe. The fact that her fear and hatred from her trauma had tainted the Light meant that it would be drained as the device tried to get at her memories.
Nagi was left helpless as Zagi took the energy and restored his Ultra form. Leaving her in a field of darkness Zagi left to attack the Earth, starting at where it all began, Shinjuku. Komon, however would not allow things to end like that way and dove into the darkness as it swallowed Nagi's form. Within the dark, Komon found his way to Nagi calling out to her the two held hands their bond creating the light that restored Nexus' powers. With both inside the giant of light who had been re-energized, and they quickly left for the city of Shinjuku, arriving to bear witness to Dark Zagi's rampage.
The evil giant was destroying the city, but Komon found that he now possessed the Light. Understanding its meaning more so than any of his known predacessors, Nagi watched as he called out the Ultra's name for the first time in the series, Nexus.
After Nexus, as Noa finally, destroyed Dark Zagi, Nagi and all of the Night Raiders continued to hunt the remaining Space Beasts, this time in public and with an expanded TLT.
Evoltruster: Nagi first draws the Evoltruster from its sheath and then extends it into the air and it shines. From an outsider's point of view, the Deunamist disappears into the light and emerges as Nexus. Nagi's rise is different from the others. It starts with the same background as the others, then an explosion of flames (representing her anger) cover the screen and Nexus is seen punching at the screen.
Powers and Weapons
- Deunamist Powers: For a time Nagi had the powers inherent to Deunamists.
- Sixth Sense: Even before becoming a Deunamist, Nagi had a sixth sense when it came to detecting Space Beasts. It was even better than the Beast Wave Sensors her team used. It is suspected that this was the reason she was chosen as a Deunamist.
- Night Raider Training: Like Komon, she is a trained Night Raider, except she is more experienced and driven in her training.
- Evoltruster: Nagi uses this device to transform into Nexus.
- Blast Shot: Nagi can use this weapon to fire energy bullets.
- Of all the known Deunamists, Nagi is not only the only female, she is also the one with the shortest on-screen time as Ultraman, transforming once, only to be defeated and drained of her power second's later.
- It was originally planned that there would a time travel adventure where Komon would discover who saved him as a child. It was to be revealed that it was Nagi who saved him in a sort of time loop.
- She is the only Deunamist that does not have her own unique form of Nexus.
- She is the only Deunamist who transforms in a similar manner to Dark Mephisto.
- Yasue Sato (Nagi's actor) also appeared in Ultraman Zero The Movie where she played the mother of Run and Nao in the past, named Mina.
- She is also famous for playing Jabi in Garo and appearing in Gaoranger of the Super Sentai series.