Ajin Wiki
Eriko Nagai
Name Eriko Nagai
Kanji 永井 慧理子
Rōmaji Nagai Eriko
Status Alive
Age 15
Gender Female
Hair Color Brown
Eye Color Brown
First Appearance Chapter 1 (Manga)
Ajin Part 1: Shōdō (Film)
Episode 1 (TV Anime)
Image Gallery

Eriko Nagai (永井 慧理子, Nagai Eriko) is the younger sister of Kei Nagai. She is a human.


Eriko is a young girl of rather short stature. Eriko has long, dark brown hair split into two braids and bangs. She has dark brown eyes and thick eyebrows. When she was younger, instead of braids she had two high ponytails, and still had the same bangs.
Most likely provided by the hospital she is in, she has shown to be wearing a white hoodie along with white pants and pink socks.


In contrast with Kei and her mother, Eriko is the most empathetic of the Nagai family. She believes there is importance in caring for people and resents those who are selfish, cold and utilitarian. However, she isn't exactly shown to be warm and welcoming and can be quite blunt herself, unapologetically stating her opinions on Ajin and loudly complaining about those visiting to interrogate her. She holds her own air of confidence, as although she initially fainted after witnessing the graphic murders of people in her hospital room, she seemed completely unfazed when speaking to Sato and Tanaka, who had subjected her to such a scene and forcefully kidnapped her.
Spending so much of her life in a hospital, it is possible that she sees more value in friendships because she herself is unable to socialize much, but this is speculation.


Eriko has suffered from a terminal illness since she was very young, hence why Kei wanted to become a doctor at such a young age. Eriko comments that she did play a lot with her brother when she was younger as well as with Kaito, and they seemed to have a closer relationship at the time. It was particularly after the incident where Kei abruptly and easily cut ties with Kaito where she began to resent him. She is hospitalized throughout most of the series.
Once when they were younger, their puppy died, and was upset when her mother called the dog just a piece of defected merchandise. Kei tells her that's just what happens with sick things. She wonders if all people die when they are "defected".


Early Manga[]

Eriko witnessing the people in her room being killed.

Her first appearance is when she is being questioned by Izumi Shimomura. She is irritated by all the people coming to interrogate her, and here she expresses disgust that someone in her family who she thought was human was actually an Ajin. She tells Izumi the story of when Kei saw the Black Ghost when they were burying their puppy (although she did not know herself what he was looking at). Shortly after, Tanaka brutally attacks the men in the room and Izumi with his IBM and Eriko passes out from shock.

Later she is seen answering questions for Sato and Tanaka and does not appear intimidated by them. She tells them that she does not resent Kei just for being an Ajin - and somewhat feels pity for the Ajin - but her brother has always been scum, cold and uncaring of others. Sato and Tanaka release her from their captivity after this and she goes back to the hospital.

Forge security arc[]

Eriko shows concern for Kei.

After Ritsu Nagai recieves a phone call from Kei, she returns to Eriko's hospital room and tells her what happened. Eriko is surprised and inquires on what Kei has been doing. When told that he "fought some terrorists" she dismisses the idea saying she can't imagine he brother being a cop, saying he is too "cold". Her mother then explains to her that her brother is not completely uncaring, but just an overly rational person who prioritises what he cares about most in the situation and focuses on protecting that. She tells Eriko it is wrong to dismiss such people as just "cold", but adds that she does not reject the humanity and compassion that Eriko and her father possess either; that’s what made her fall in love with their father . Eriko begins to cry and admits that she is worried about her brother, and lays down on her mother's lap.

Iruma base arc[]

In chapter 59, when TV news cameras broadcast the image of Kei standing on the runway at Iruma base, Eriko is shown very briefly to be reacting with surprise.


Kei Nagai[]

Eriko's early perception of Kei.

He is her brother. Even earlier on, she seemed to notice that Kei was doing everything for his own benefit rather than because he cared about others. She holds resentment to him for being a cold person and holds no sympathy for him when she discovered that he is an Ajin. It seems the main reason she resents him is due to him cutting ties with Kaito in their childhood. Although Kei initially wanted to become a doctor to cure her illness and asks Sato if she is okay after they had kidnapped her, he barely thinks about her well-being later on in the manga. However, Eriko admits she is worried for her brother in chapter 59.

Ritsu Nagai[]

Her mother. Eriko views both her mother and brother to be too cold and rational, and seems to be hurt by her words when she talks about the dog as it was something materialistic and easily replaceable; a mere deficient item, rather than a living being. It was also her mother who told Kei to delete Kaito's number. Despite this, her mother does spend a lot of time with Eriko in hospital, and comforts her when she expresses concern for her brother, so they do have some extent of a friendly relationship.


Eriko, Kei and Kaito would play together when they were very young. Cutting ties with Kaito is one of the main reasons she comes to resent her brother. It is implied that she has, or previously had, some kind of crush on Kaito as she thinks about him often and sometimes blushes when she does. How much they have been in contact with each other is unknown, but it is likely that it is not much or barely any at all since they were children. Nonetheless, they still have each others' numbers saved on their phones.


  • "Why are you always so quick to make things black and white? What's wrong with caring for everyone?!" (to Ritsu Nagai, chapter 44)


  • Her surname, when using the kanji 永井, means (ironically) "eternal well".
  • Her illness was never revealed for unknown reasons.