Ao no Deracine

Shiina Atsushi, a Japanese-American boy, lives in Japan during WWII. He comes across a Chinese girl, collapsed among the debris of a collapsed building, with a strange glowing symbol on her back. She claims she's from another world that has been destroyed. As she attempts to leave, the military arrive and demand she go with them. Who is this mysterious girl? What will young Atsushi do?