Shingo Hiromori

The year is Universal Century 0088. Directly after the end of the Gryps War, Haman Karn and her army of Zeon remnants on the asteroid Axis begin their quest of reviving the lost empire of the Zabi's, and proclaim themselves as the Neo-Zeon. With the Earth Federation as hapless as ever, only the Anti-Earth Union Group (AEUG) is able oppose the plans of Neo-Zeon. In need of all the help it can get after being decimated in the previous war and losing many of its key members, the AEUG ship Argama en (myanimelist.net)

A spaceship is lost near the forbidden planet of Inferno II. Some years later, a second ship with a crew of nine gets there and encounters a monster that rapidly makes mince meat of most of them. The sole survivor, Makurou Kitazato, must destroy the monster before it can surprise a third ship that is already en route. (myanimelist)

Marina is a mermaid who is in love with Prince Justin, a human prince from a kingdom on the shore. Marina saves Justin when he almost drowns after a chase from a giant Cyclops and a shipwreck attack from a three-headed sea serpent. She then makes a deal with Hedwig the sea witch to become human temporarily to try to win Justin's love. (Wikipedia)

Prince Jorudi with his brother, Hai Sharutatto, are fighting against their father, Madaru, with his evil world domination ambition using giant robots. However, both Prince Jorudi and his brother's goals might not be the same, even though they are both fighting their father, a tyrant. While Prince Jorudi's goal is to save the world from his father's ambition, Hai Sharutatto plans to take over his father's place, and therefore, he sees Jorudi and their sister, Chururu, as nothing but rivals.