Does the US enforce Japanese copyrights? Or did Konami also register it with the Library of Congress so it had protection here?

I can completely ignore the time it "was extended." Copyright exists from the time you've registered it. You can play mental gymnastics here if you like but the law is particularly cut and dry.

The law isn't something that exists in a vacuum. It's meant to convey the will of the people. Show me where the will of the people demands corporations get copyright protections longer than a human lifetime?