The Vertical City Cage

After resources are depleted in the future, humanity is trapped in a vertical city known as the “Cage”:

The lower-level “Rust Belt” (floors 801–1000) struggles amid toxic fumes and poverty. The middle-level “Gear District” (floors 201–800) has been reduced to a production tool. The upper-level “Cloud District” (floors 1–200) monopolizes all resources. Beneath them lies the “Core District” (underground levels 1–10), a “spatiotemporal cage” used as a prison for “class rebels.”

Ais, a girl from the lower levels, is thrown into the “spatiotemporal cage” in the Core District for resisting oppression. There, she meets physicist Darion and Vera, a rebel from the upper levels. The three discover that the cage and the city’s energy supply are intertwined, and that the upper levels use spatiotemporal technology to suppress dissent. They also uncover the truth behind the “Great Collapse”...

A technician from the middle levels breaks through spatiotemporal turbulence and the blockade of the mechanical army, destroying the cage’s core and triggering the collapse of the city’s class system.

At last, the old order crumbles, and the survivors rebuild civilization atop the ruins.