Fighting General Daimos (1978)

The planet Baam has been destroyed, and its inhabitants are towards the Earth. Their leaders starts peaceful negotiations for the purchase of land for emigration. When the leader is assassinated by his second-in-command, the diplomatic delegation from Earth is framed for the murder. The Baam start a war against the Earth. The super-robot Daimos and its pilot Kazuya Ryuzaki are the Earth's best line of defense. Kazuya is conflicted because he has met Princess Erika of the Baam and fallen in love with her. He is well aware that Erika and her people are not malevolent by nature.