Princess Arenanda, a royal of unspecified lineage, embarks on the luxury cruise ship *Rosebud* alongside her sister, Princess Darenanda, during its maiden voyage. Tasked with safeguarding the Muscle Carrot—a potent elixir designed to amplify superhuman abilities for noble warriors in Japan—their journey is disrupted when hostile superhuman forces assault the vessel to seize the artifact. Arenanda escapes the onslaught alone, compelled to seek aid from Mantaro Kinniku (Kid Muscle) and his companions to liberate her captured sister and recover the stolen elixir.

Though Mantaro resists engaging in high-risk missions, his resolve shifts upon hearing of Darenanda’s striking beauty, motivating his involvement. Arenanda’s tenacity anchors the mission, balancing her urgency to protect the Muscle Carrot with her dedication to her sister’s survival. Surviving the initial attack, she proactively secures allies, directly enabling the protagonists’ airborne infiltration of the hijacked *Rosebud* via a Cessna. This bold maneuver initiates a decisive clash against the occupying superhuman army, driven by Arenanda’s unwavering resolve to rectify the crisis she helped ignite.