Shizuka Namino infiltrated Earth's government as Secretary to the Prime Minister while secretly spying for the alien Mazone. As part of her mission, she staged an assassination attempt on the Prime Minister, framing Commander Kiruta for the crime. After securing Kiruta's imprisonment, she manipulated his personal feelings to gain his assistance in escaping and convincing him to request sanctuary for her aboard the starship Arcadia. Her core objective onboard was to identify the ship's mysterious forty-second crew member and disable the vessel from within.

Captain Harlock eventually uncovered her true allegiance, leading the Mazone Queen Lafresia to order her forces to abandon Shizuka. Despite her betrayals, Harlock granted Shizuka freedom and intervened to save her when Mazone forces attempted to eliminate her. Torn by guilt over her mission failure and a growing admiration for Harlock's honor, Shizuka deliberately provoked Harlock into killing her during a confrontation.

Harlock chose not to reveal Shizuka's espionage to Commander Kiruta, who held genuine affection for her. Instead, Harlock informed Kiruta that Shizuka died heroically fighting the Mazone fleet.

In the OVA "Endless Odyssey," a character named Shizuka Namino, sharing the original's visual appearance including her distinctive dress and pendant, appears as a holographic assistant to Dr. Daiba. This version possesses dark hair consistent with the manga depiction of the original character and exists as a separate narrative incarnation distinct from the earlier storyline.