Tenkuu Shinpan

Yuri Honjou finds herself on the roof of a skyscraper after witnessing a masked figure murder someone in front of her. There are no streets she can reach and no path to the ground. The entire world is a network of high-rise buildings connected by suspension bridges, patrolled by masked killers who drive their victims to death or attack them directly.

Yuri learns that her older brother Rika is trapped somewhere in the same place, making finding him her first goal. To reach him she must cross the bridges, survive the masks, and understand the rules governing this impossible world. Some masked figures are not killing by choice, some ordinary people are more dangerous than they appear, and a larger purpose lies behind gathering everyone above the city. Yuri gradually stops thinking only about escape and starts considering how to destroy the system itself.