Planet Robo Danguard Ace

(from ebookjapan):

Prometheus, the tenth planet in the solar system, is a distant planet that circles the sun in a 170 million year cycle. In an attempt to develop Prometheus, which is said to have an environment almost the same as that of the Earth, the human race launches an emigration plan to Prometheus, but it ends in failure due to the betrayal of the pilot, Ichimonji Fumitetsu.

Ten years later...

While Führer Doppler is working to make Prometheus a planet where only the chosen elite rule, Ichimonji Fudetetsu's son Takuma, though regarded as a coward's son, is honing his piloting skills under Dr. Oedo. Oedo's group is outnumbered by Doppler, but they have a trump card in the form of the giant robot "Danguard A"!

A SF romance by Leiji Matsumoto of "Galaxy Express 999"!