Ishiro Honda was in top form in 1957, having already helmed Gojira (1954) and Rodan (1956). For The Mysterians, a story of invading aliens and the resistance movement to stop them, it was decided that Toho would use its widescreen technology, TohoScope. This, combined with its fantastic color palette, makes for one beautiful (and fascinatingly deep) science fiction movie.
Strange natural phenomena plague the island of Honshu, culminating in the appearance of a giant robot, the Moguera. This bird-faced behemoth (which appears to be wearing samurai armor) trashes a village in the mountains, heralding the appearance of the Mysterians, a race of humanoids from the “Mysteroid,” a belt of asteroids between Mars and Jupiter. Once a planet, it was destroyed by the aliens when they discovered atomic warfare. Now they want a small piece of Earth land on which to build a base, and some Japanese women to help repopulate their decimated race. Shocked faces and steely resistance ensue.
The Mysterians owes much to American science fiction movies of the time. Like The Day the Earth Stood Still (1951) and Invasion of the Body Snatchers (1956), what masquerades as good ol’ entertainment is actually an allegory for current events. This is strictly my interpretation of things, mind you, but from where I’m sitting, The Mysterians is an anti-American Occupation diatribe.
Breaking it down:
1) Men with advanced (read: atomic) technology land on the home islands and destroy civilian targets.
2) Said men want a small piece of land on which to build a base.
3) They also want to breed with Japanese women, much as the American GI’s did.
4) Lastly, their secret purpose is to take over Japan for themselves. America never wanted Japan’s land but our cultural influence was unmistakable.
Of course, the American Occupation was already over at the time The Mysterians was released in 1957 (at least on the main islands), but the aforementioned cultural takeover was ongoing. Also, the secret security treaty between Japan and America was still in place, and would be renewed in 1960, prompting a number of more overtly anti-American films to be made.
This is all conjecture on my part, much like my assertion that Gappa The Triphibian Monsters (1967) is actually about ugly American tourists run amok in Japan. But hey, the best science fiction is often working on numerous levels. Or maybe it’s just my white guilt.