Yet another expansion of the Marine Boy series. This time 65 episodes were added to the 1966 series and all 78 episodes were sold to the US. The broadcast history of the show in Japan was slightly more complicated, with only the first 36 episodes of the 78 shown at first but later on all 78 were shown, out of which 65 are contained in this entry and 13 in the Ganbare! Marine Kid series. Marine is now equipped with an underwater boomerang, a hydrojet, and the mermaid Neptuna/Neptina has become his girlfriend. Some previous episodes from Ganbare! Marine Kid had their footage recycled in part for this series. (Source: The Anime Encyclopedia)

Pero, a sword-wielding cat-in-boots sentenced to death for sparing a mouse, escapes his execution and embarks on a journey. Along the way, he teams up with a company of bandit mice and Pierre, a gentle orphan who has been cheated out of his inheritance. When Pero learns that Princess Rose is seeking a husband, he becomes determined to make sure that Pierre is the one chosen. However, Princess Rose is forcibly betrothed to the wicked ogre Lucifer! Pero begins to spin a web of lies to enthrall Rose with Pierre, but Pero's boasts are far from the truth. Pierre has to keep up with Pero's bold image of him but is frightened, because while Princess Rose is charming, loving her means going against the Devil's wishes. [Written by MAL Rewrite]

Pero, a sword-wielding cat-in-boots sentenced to death for sparing a mouse, escapes his execution and embarks on a journey. Along the way, he teams up with a company of bandit mice and Pierre, a gentle orphan who has been cheated out of his inheritance. When Pero learns that Princess Rose is seeking a husband, he becomes determined to make sure that Pierre is the one chosen. However, Princess Rose is forcibly betrothed to the wicked ogre Lucifer! Pero begins to spin a web of lies to enthrall Rose with Pierre, but Pero's boasts are far from the truth. Pierre has to keep up with Pero's bold image of him but is frightened, because while Princess Rose is charming, loving her means going against the Devil's wishes. [Written by MAL Rewrite]