: The bubble acts as a physical and metaphorical barrier, exploring how abandoned youth create their own societal rules and bonds within a "lost" city.

: Hibiki and Uta are bonded by a unique sound that only they can hear, which serves as a central mystery of the film. Literary and Artistic Influences

: A sunken, bubble-encased Tokyo where young orphans and parkour enthusiasts live and compete in dangerous team-based "Tokyo Battle" competitions across the skyline to trade supplies.