Yonah was the sister of a young Nier in NieR RepliCant, and daughter of an older Nier in NieR Gestalt (NIER). During the beginning of NieR, she and Nier were hiding in a supermarket from the attacking relapsed Gestalts.
After dispatching three attacking shades, Nier goes to check on Yonah. After reassuring Yonah that he'll protect her, Nier checks the entrance, only to find more shades. Nier succeeds at fending off three to four shades before being knocked to the ground. He then decides to give in to the Black Book, trading his soul for power. Nier then fights dozens of shades using the power of the book, easily killing all of them. When he goes back to check on Yonah, she offers him a cookie. Yonah starts uncontrollably coughing, when a bunch a markings start travelling up her body. She reveals she touched Grimoire Noir to help her father/brother and turned into a Gestalt, and began to relapse.
1,412 years later (1,312 in NieR Gestalt) when Nier and his allies come to save Yonah from the Shadowlord, Yonah is seen in a comatose state. The Shadowlord then appears before the group and battles them, nearly losing to Nier, but Yonah then wakes up, calling for her father/brother. As she and Nier walk towards each other, Yonah then passes him and continues toward the Shadowlord. It is revealed that she is the true Yonah, whom the Shadowlord (Gestalt Nier) was trying to put back in her body to prevent relapsing. She begs him to stop and give up. She states that she hears Replicant Yonah's cries for her father/brother. Gestalt Nier begs her not to leave, but she sadly tells him she loves him before leaving her body, presumably dying in the process.
- Yonah is the only character seen as a true human in the main game.
- She is the only character in NieR to appear only in the prologue and part two.