Reiko Tsuruyama, an elderly woman, is a regular at Cafe Poirot, interacting with staff members Azusa Enomoto and Toru Amuro. Online, she games under the alias "REI," using white-colored equipment and communicating cheerfully and politely with fellow players. Her gaming activities include tackling event quests and teaming up with others, like the player "YUUYA" (later identified as Yuuya Kazami).

One evening at Cafe Poirot after closing, Reiko reveals to Azusa and Amuro that she started gaming to stay current with trends but developed a genuine passion for it. She describes her "triple face" existence: sometimes an Ikebana teacher, other times a ballroom dancer, and embracing her "true self" as a gamer. This disclosure leads Amuro to recognize parallels with his own complex life.

Her alias "REI" derives from the character "Rei" (零) in her name, Reiko. She remains unaware that her gaming partner "YUUYA" is Kazami, a security police agent, just as Kazami initially fails to connect her online identity to Amuro's cafe customer. Her interactions at the cafe and within the game underscore recurring themes of concealed identities and dual lives among the narrative's characters.