Gunners

In a parallel 21st century Japan, an enemy with incredibly advanced technology attacks mainland Japan from Hokkaido, shattering the Japanese Defense Forces and their American allies. Japanese military scientists use what enemy technology their troops can capture to create their own mecha to fight off the enemy's advance. But what does this have to do with a boy named Yuu, a mechanical genius with motion sickness, and his separation from his younger sister for over 7 years? Why does she suddenly appear after all that time, dressed as a miko and shadowed by a fox, at the temple where Yuu lives with his uncle? Is she who she says she is?