Read manga: Sakasama No Patema: Another Side

manga
Summary:

A floating ring has been passed down through Mikko's family for generations. Her grampa 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... This is the side story to the film Inverted Patema.