WMG / Daimos

The reason for Miwa's bigotry is because he grew up in post-World War 2 Japan

Firstly, I would like to start by stating that the anime makes several references to World War 2.

• The UN is frequently mentioned in the anime and some characters (such as Miwa, Dr. Ryuzaki and Dr. Izumi) are members of it. The UN was created post-World War 2 to prevent conflicts like it from ever happening again, being built on the concept of the pre-existing League of Nations.
• While Kazuya is looking at the memorial of the fallen, astronauts of various different nationalities are seen. This is probably a nod to the space race that happened during the Cold War, which was directly after World War 2.
• Miwa also has a hydrogen bomb. For a hydrogen bomb to exist, there must have been various different types of experimentations of prototypes. The first nuclear bomb in Japan was developed during - you guessed it - World War II.

The Roman Robo Anime Climax Selection states that Miwa's age at the time of the story is 45. Richter led the Baam invasion in 1999. That means Miwa's birth year is 1954.

1954 was just a decade after the end of World War 2. Now, in Japan, it's common knowledge that the war ended with Hiroshima and Nagasaki. The bombings ruined Japan and the effects of radiation would persist and claim many more innocent lives.

I imagine that Miwa, at a young age, had to witness his parents and grandparents grapple with the horrors of the war. Perhaps he lost them to the bombings, or maybe they were innocent civilians unfortunate enough to get hit by the radiation and succumb to it.

Miwa likely grew up with a lot of guilt being the only one in his family being lucky enough to be unharmed from the bomb. There is also a possibility that they did escape unscathed, but Miwa wanted revenge. Maybe Miwa's family was thriving before the war, and the bombings forced them to downgrade their standard of living or become refugees.

If Miwa's family was involved in some of the more disturbing parts of Japan's role in the war, they could have faced stigma over this fact. If they were taken prisoner by the allies, it would be a matter of shame to his family name.

In the original Japanese (I'm not sure if the dubs caught this one) Miwa's catchphrase is "You unpatriotic people!", which he often yells at Kazuya. It can be read as a nod to Miwa's nationalism, but with all the references to World War II, it takes on another meaning.

When the Baam invaded, all Miwa could think of was the fact that they were people of a foreign land bringing destruction to the shores of their country. Miwa has long had a fear instilled on him of foreigners and their weaponry, and when he looks at the Baam, all he can think of is the fact that they bear an uncanny resemblance to the very nation that brought Japan to it's knees. Not helping the fact that the Baam are mostly Caucasoid (they're based on Rome, after all) and their leader is a blonde, muscular white guy (which is the common stereotype Japan has of Americans). The Baam's main method of terrorism is to use large machines - evoking the image of airships used by Americans during the war, and many a Mecha Warrior have the power to cause explosions. One episode literally focuses on a child blinded by the after-effects of a Mecha Warrior, which is an uncanny parallel to the effects of radiation the bombs had on the human body.

If this isn't the first time Miwa has seen such atrocities....no wonder he hates all the Baam and wants to see them exterminated.

• There is indeed one record of a Nagasaki survivor with the surname Miwa.

Nana is adopted

Nana is said to be Izumi's granddaughter, but not only are her parents never seen, Izumi never mentions havung children. Granted, the predecessor anime had a similar case to this with the stating that Hamaguchi was Ippei's maternal grandfather (not depicting this in the anime and only stating it in the Roman Robo Anime Climax Selection), but Ippei's parents were at least shown in his flashback.

What supports my theory is that Nana has blonde hair and blue eyes, in contrast to most characters that look fairly Japanese. The Robot Romance Trilogy typically avoids Mukokuseki - in Voltes V, not only does the Big Falcon cast look exclusively Japanese, but the one character with an odd hair colour for a Japanese man turns out to be an Alien Among Us). Kyoshiro, while passing as black, can also pass as Japanese because dark-skinned ethnic Japanese people exist. Blonde-haired blue-eyed ones don't.

It could also be why she doesn't view her crush on Kazuya as immoral. Since her, Kazuya and Izumi don't have any connection by blood, from her perspective it's no different from pursuing someone who isn't related to you.

Richter and Erika's mother was deliberately killed

For Olban to wait until Erika and Richter were of ruling age sounds like a pretty poor plan, as by then they would be capable enough of inciting revellions and acting on their own. The Baam are also stated to have advanced technology, so for the palace to "suddenly" catch on fire seems unusual. It's likely Olban had Georiya hope to kill off Leon and his heirs, but failed.

Margarete was chosen for her skills in poison

Margarete conveniently knew how to get her hands on a serum to cause Erika to faint, and was also seen tending to the wounded in New Zealand. What if Leon, after the death of Roji, hired her so that she could be somewhat of a bodyguard/stealthful protector to his kids?

The Baams are related to Garuda

The Baams are named after the Brahmins. Their custom of having circular objects on their foreheads is also similar to the Brahmin custom of applying a red dot to the head, and they're both somewhat priestly classes. Garuda is also taken from Hindu mythology, being named after the Eagle King. Perhaps at one point Campbell and Baam were one nation and split, but the Hindu influence stayed.

• Alternatively, a long time ago, some Hindu astronauts went to those planets and spread their culture there, inspiring them both.