This is a big, cheesy space opera that makes about as much sense as an anime. In the far future, somehow human space is divided between a Japanese empire that has reverted to feudalism, and an "Amerikan" empire whose planets all have names like "Texas," "Kansas," "Maryland," etc. There is some mention of other nationalities as well -- apparently the Chinese, Russians, Spanish, etc., all went out and colonized space, and each forged separate little empires in which all of their planets are characterized by national/ethnic stereotypes from centuries earlier. Then they all get conquered by the Japanese, and it's left to the Amerikans to fight them.
The space battles are fun, if improbable. Kato makes up a lot of nonsense technology so that somehow, ships with beam weapons and force fields still wind up engaging in boarding actions where the crew fight with swords.
The characters, the politics, the technology, the setting, is all completely absurd. It's like Kato was allowed to publish a novel based on this neat epic he imagined when he was fourteen. But like lots of fourteen-year-old fantasies, it was still kind of big stupid fun.
It's been years since I read this book. I understand there was a hard-to-find sequel; I have no idea if the promised five-volume series ever materialized.