Monster Strike the Movie: Sora no Kanata

Thirteen years ago, a section of Tokyo abruptly broke away and began floating in the sky. The city was divided into "Old Tokyo," the part suspended in the air, and "New Tokyo," the part remaining on the ground. With no way to communicate or travel between them, the two Tokyos drifted apart over the years. Then, a young girl discovers that Old Tokyo is destined to crash back to the earth. To avert disaster, she embarks on a dangerous journey from Old Tokyo to New Tokyo, determined to warn its citizens before it’s too late.