With so much to put their heads into, I fail to see any merit in the endeavor. Or in simpler terms, bull sh!t.
It's quite simple, really. Any military technology Japan might develop which would be effective against a technologically advanced extra-terrestrial threat would also be effective against a possible human threat (aka the Chinese and Koreans). Moreover, claiming that the research and development is aimed at a theoretical extra-terrestrial threat allows them plausible deniability to counter the inevitable charges and propaganda by China and Korea that Japan's military programs are aimed at them.
They really should be watching out for Algore!