Sakasama no Patema: Another Side

This is the side story to the film Inverted Patema.

A floating ring has been passed down through Mikko's family for generations. Her grandpa told her that the ring bears a promise of reuniting with lost ones who departed to the "other world." Mikko explores her world—an endless network of tunnels—in hopes of finding the "other world" one day...

(Source: MU)