Reileen Kawahara is the sister of Takeshi Kovacs.
Reileen was born on Harlan's World and is of mixed Japanese and Eastern European decent. She has one older brother, Takeshi Kovacs. Although she doesn't share her older brother's last name, her father is shown in flashbacks to be a white male so it's safe to assume that while Takeshi took his father's name, Reileen would have taken her mother's, as their mother was of Asian decent from her family photo she shows to Takeshi. Rei and her brother grew very close living under their abusive father, often exploring the planet's wilderness together and telling scary stories like the Patchwork Man. Eventually, following the death of their mother, Takeshi was forced to kill their father after he threatened to harm Rei. Taken into custody, Takeshi joined the Colonial Tactical Assault Corps in the belief that his sister would be taken care of. Instead, Reileen was sold to the Yakuza and became one of their enforcers. During a CTAC raid, Reileen met Takeshi for the first time in ten years. During the reunion, CTAC officers tried to kill Rei, prompting Takeshi to turn on them to protect his sister. Reileen did the same for Takeshi, turning on her Yakuza masters.
Now fugitives from both factions, Rei and Takeshi fled to the wilds of Harlan's World, falling in with Quellcrist Falconer and her Envoys. While Takeshi became dedicated to the cause, Reileen was less enthusiastic. Out of jealousy for Quell, Rei ultimately betrayed the rebels to the Protectorate and turned on Quell herself during the escape, destroying their shuttle with an orbital laser strike. Though presumed dead, Rei had actually managed to survive the explosion, using her new wealth to become one of the most powerful meths by 2384.
Throughout the series
While deciding whether or not to solve Laurens Bancroft's murder, Takeshi has a vision of his sister and Quell, both asking him what he should do.
Takeshi later encounters Rei at a museum exhibit about Quell and the Envoys, posing as a young schoolgirl. Though she says a familiar line from their mother, he ultimately does not recognize her.
Reileen attends Bancroft's party, posing as another meth named Clarissa Severin. Her gift for Bancroft is a snake with the mind of a convicted serial killer.
As Hemingway, Reileen meets with Dimi the Twin, ordering him to leave Takeshi alone, though he adamantly refuses. Hemingway later meets with Takeshi (disguised as Tanaka) in the virtual world. Though Rei slowly begins to recognize her long-lost brother, the meeting is cut short when Dimi attacks the cafe Takeshi is visiting.
Realizing Dimi has gone against orders, Reileen travels to Panama Rose Fightdrome and singlehandedly rescues Takeshi, killing many people in the process.
Rei takes Takeshi back to Head in the Clouds and nurses him back to health. Though Rei desires to put her brother in a new sleeve to save his life, Takeshi insists on remaining in Elias Ryker's sleeve as a promise to Kristin Ortega. Once recovered, Takeshi and Rei catch up on lost time.
Reileen personifies the worst traits of a meth, and all the qualities that Quellcrist Falconer warned about. She is arrogant, manipulative and self-centered, with a massive ego and "love" for her brother that verges on the psychotic.
She believes she has made herself stronger and better by getting rid of things she sees as weak- mainly empathy, compassion and human emotions. As a consequence, however, she is somewhat ignorant in certain matters. She claims to love her brother, but does not seem to grasp what love means and the bonds that it can form, as Takeshi had done with allies past and present.
Reileen Kawahara, in the book the series was based on wasn’t Kovacs’ sister. Hence their different surnames.