The story is set in the Great Collapse era, a near-future world where civilization has been pushed to the brink of destruction by massive disasters and warfare. Society has deteriorated into chaos, with rampant violence involving humanoid weapons and the spread of slavery.

The narrative begins by following Zoe, a young female detective struggling to maintain public order. Her life changes when she helps an elderly woman caught in a mafia dispute. The mafia retaliates by deploying a giant doll-like weapon, the Runner, to eliminate them, dragging Zoe into a much larger conflict. This seemingly helpless old woman harbors a dangerous secret, as she is actually the leader of a private military organization known as the Iron Sheep.

The central conflict escalates as the old woman, named Olga, is known as the Witch of the Slums. She and her subordinates, including a Runner pilot named Masaki, fight to dismantle the slave trade and liberate the oppressed. They clash with powerful slavers who deploy formidable enemies, including a skilled pilot named Ten.

As the series progresses, the Iron Sheep engages in covert operations to rescue captured comrades from enemy strongholds. The final arc involves a full-scale invasion by Ilya, the mastermind of the slave trade, who attacks the Iron Sheep headquarters with advanced heavy weaponry, leading to a decisive final battle between him and Olga.