Luna Kozuki fights alongside Casshern against robotic threats across multiple Casshan franchise iterations. In the 1973 series, this fifteen-year-old wields the Magnetic Field Gun (MF Gun), a critical weapon against robots developed by her scientist father. Her combat skills make her an essential fighter, not merely a support figure. As Casshern's childhood friend and love interest, their partnership drives the narrative during missions confronting the Android Army and exploring hostile environments like robot prisons and battlefields, often aided by the robotic dog Friender.

Her appearance consistently features blonde or yellow hair and blue eyes, with practical combat attire varying between adaptations. The 1993 OVA *Casshan: Robot Hunter* portrays her fighting machine overlords, showcasing defiant courage early on during a robot prison camp uprising. Her actions remain linked to the human resistance opposing the Black King. The 2004 live-action film *Casshern* includes her in the core trio, depicting a determined participant in the conflict against artificial forces, though her character arc diverges from the original storyline. Luna Kozuki does not feature in the 2008 series *Casshern Sins*.