Ryuu is Hal's childhood friend, sharing a significant history from their youth. Both were sold into slavery as young boys but escaped, leading them to collaborate in illegal activities like theft and dealing stolen goods to survive.

Their shared background of poverty and abandonment shaped Ryuu's motivations. Hal faced parental abandonment due to medical debt, driving both characters toward crime to avoid financial ruin. Ryuu became involved with loan sharks, reflecting their ongoing struggles with debt and illegal dealings.

During the film's events, Ryuu encounters the robot posing as Hal. He later ambushes the robot Hal and Kurumi during a festival, demanding they "cash Kurumi in" to recoup financial losses. This confrontation escalates into a chase, culminating in Kurumi falling into a river. During the struggle, Ryuu attacks the robot Hal and delivers the pivotal revelation: "Kurumi is already dead!" and "Wake up! Try to remember!" This forces the robot—and the real Hal, experiencing laser-guided amnesia—to confront the truth that Kurumi perished in the plane crash, not Hal.

Ryuu's actions underscore his role in perpetuating a cycle of crime that contrasts with Hal's attempts to reform. His aggressive intervention ultimately catalyzes Hal's acceptance of reality, though Ryuu remains entrenched in his destructive path.