Reya Morikage

She informs Ikeno that the infection has spread far more widely than he assumes, so becoming a zombie is a better decision from the point of survival.

"Humans have emotions, so they can't just shoot someone so easily. They also hesitate to use a precious Vaccine card for someone else. But while they hesitate and hold on to their cards, the number of zombies keeps increasing. Once someone becomes a zombie, there's no reason to hesitate to use a Zombie card." — Rei explaining how human psychology works in the "Zombie Hunt" game

According to Rei, if the infection were to spread exponentially, it would take only three turns for the zombies to surpass the majority. With that in mind, she offers Ikeno a deal: become a zombie instead of killing her. Ikeno decides to use his Shotgun card instead, and Rei smiles. After Ikeno comes back to the common room in shock, he states that Rei deceived him. Then Arisu finds Rei sitting in the same chair with her head down, so he assumes she was eliminated, but the moment he calls her name, she turns around and looks at him. Then Arisu and Rei play a mini-game against each other, and Rei wonders why Arisu decided to choose her as an opponent. Arisu asks who will win in her opinion, and Rei confidently claims that the zombies have all the chances, because the game implies only two outcomes: either the number of zombies increases exponentially, or all the humans kill all the zombies. Arisu seems to have come to the same conclusion, so he attempts to make Rei admit that she has never been a zombie. He breaks down her strategy of building trust based on a lie, securing her spot in the safety barricade, and reveals that Ikeno was not able to shoot her because she was not a zombie. Then Arisu turns over a Zombie card, and Rei is visibly shocked. She explains that her barricade plan was not meant to be a trick, and she honestly believed that humans had a chance, so she preferred not to turn into a zombie too early.

She confirms this understanding and elaborates that refusal to follow the plan later on will result in death. She also hugs Tetsu during her monologue, and he is visibly uncomfortable.

"We repeat the same process and promise with multiple people. And in this way, we create a unified group built on trust. If you become a zombie, we will cure you with the vaccine." — Rei's further clarification

In response to Arisu's observation that they have only one Vaccine card, Rei intends to invite other players who have the same cards. When Tetsu objects that there are not enough cards for everyone, she confidently points out that the actual number of Vaccine cards is unknown, which means it is enough to make everyone believe that the number is sufficient. At the end of her speech, she confesses to being a Zombie with a Vaccine card herself.Arisu and the others spread out and explain Rei's strategy to the different participants. Rei continues to be an observer and witnesses the first victims of her plan when players start killing the zombies instead, but remains indifferent to their fate. Later, she finds another body near a game table, smiles, and claims to care only about the safe barricade they have created. Arisu insists that the barricade is in danger now, which amuses and excites Rei.

"Now it's starting to feel like a game!" Rei is present when Ikeno orders Nobu to kill the zombie who infected Masato, but she avoids eye contact with the others indifferently and does not participate in the argument. While casually walking around the facility, she encounters Masato, who is running away and asking her to use her Vaccine card on him. She does not have enough time to react before the players catch Masato, while Ikeno and Kazuya corner her. Ikeno puts his hand on her shoulder, fully intending to play a mini-game against her and eliminate her.

During the game, Rei is relaxed and cheerful, spinning in her chair.

Prior to her arrival in the Borderland, Rei was a university student interested in anime. Same as the other participants of the Joker Tournament, Rei had played the games before, making her Sojourn in Season 3 a return to the Borderland rather than her first visit. However, the games she experienced in the past were not the same ones faced by Arisu and his group. Since Borderland games are created and overseen by individual Citizens, their scale, rules, and format vary depending on who hosts them. Therefore, Rei's earlier participation took place under different Citizens, resulting in a distinct set of challenges. After getting transported to the world of deadly games, Rei participates in multiple challenges of various difficulties. In order to join the "Zombie Hunt" game, she should have finished at least one more challenge beforehand. When Arisu finds two women with Zombie cards and brings them to his team, searching for a way to cure them, Rei joins the group and introduces her survival plan that does not involve killing anyone. "Just make a group where everyone promises to always use the vaccine card to cure each other. Even if one of the members turns into a zombie, you will make sure to cure that person. Then, have them tell you who infected them with the zombie card, and threaten that you will definitely shoot that person. If you do that, the zombies will be too scared to approach this group." — Rei's plan

She uses Tetsu as an example for further explanation and gives him two conical flasks with differently colored contents, labeling one as a Zombie card and the other as a Vaccine card. She points out that if, while being a zombie, a player promises to use their Vaccine card on another zombie, they would open themselves to being attacked by a Shotgun card. Arisu quickly summarizes that Rei's proposal is to make an alliance with their opponents by using some players as hostages.

Rei is portrayed as a playful, slightly sadistic individual, who enjoys difficult, "more real" games. She does not care about the casualties as long as her own survival is guaranteed, and she does not mind deceiving other players, nor does she seem to have any difficulty reading them. However, over the course of the story, she develops a certain attachment towards her teammates, and their fate visibly affects her.

After being saved by Arisu, Rei decides to join his team out of a sense of indebtedness. While she does not form a strong connection with any of the team members, she is willing to work with everyone.

Rei is good at both following instructions and devising strategies to clear the games, and she is not the type to blame others.

Rei Morikage is studying to become an animator.