Reileen Kawahara is the sister of Takeshi Kovacs. During their childhood, Takeshi was forced to kill their Father after he threatened to kill Reileen. Taken into care, Takeshi joined the Colonial Tactical Assault Corps on the understanding 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 years. During the reunion, CTAC officers tried to kill Reileen, prompting Takeshi to turn on them in defence of his sister. Reileen did the same for Takeshi, turning on her Yakuza masters.
Both fugitives, Reileen 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.