Ryu is Hal's childhood friend and former partner in crime. During their youth, both belonged to a gang, committing theft to settle debts incurred by Hal. Their illicit association persisted into adulthood, with Ryu maintaining connections to loan sharks and illegal enterprises. After Hal forms a relationship with Kurumi, Ryu persistently tries to lure Hal back into their criminal world, opposing Kurumi's efforts to reform Hal and help him build a legitimate business.

Ryu initially appears unaware of Hal's supposed death in the plane crash when encountering the robot impersonating Hal. Later confrontations reveal Ryu's knowledge of Hal's catatonic state and the truth about Kurumi's death. During a festival, Ryu attempts to coerce the robot Hal into surrendering Kurumi (actually the robot Q01) to settle outstanding gang debts, sparking a chase. This confrontation culminates near a river where Ryu physically attacks the robot Hal, explicitly declaring Kurumi dead to shatter Hal's delusion. Ryu's aggressive intervention forces Hal to confront the repressed reality of Kurumi's death in the crash.