One logic barrier is: why do the Neptune Raiders insist on attacking the only place on Earth that has an electronic barrier? Only that area of the world has one, yet the Neptunians never think of invading Mexico or Southern Africa, where the Earth resistance would be less.
shareI think somewhere in the movie there is some dialog that asserts that other major cities have electro-barriers as well. Something about cities all over the world countering the weather attack (the premature winter) with by radiating heat from the electro barriers. I'm not 100% clear on this because I think the movie had put me in a coma by that time.
Hoever, since this is an extremely Nippon-centric movie, and since the screenplay was written for 9 year old Japanese children, all the action takes place in Japan. I guess the assumption behind the story is that if Japan fell to the Neptune man, then the rest of the world would have no chance, so the "Neppies" attacked there first.
It's funny that when Americans make movies like this (Independence Day, for example), people get offended that it's Amero-centric. You know, "Those Yankees think they're the only ones who can save the world!"
But everybody does it. Here it's Space Chief, in Mexico it's El Santo, etc., etc., etc.
After all the alien invasions the Japanese have foiled in movies and TV series you'd think aliens would leave Japan for last not start there.