Kumaso serves as the doctor of the Upper World, though he's far from a loyal servant. He's quietly orchestrating a coup against Sumeragi, the mechanical ruler of this realm—a being literally composed of interconnected human brains.
Years ago, Kumaso was ordered by Sumeragi to conduct experiments on four orphaned sisters who'd been raised in his medical facility. The girls—designated Z01 through Z04—were like family to him, which made what came next devastating. Three of them couldn't handle the strain of the experiments. Z02, Z03, and Z04 didn't survive. Z01 was the sole survivor, and she's become Kumaso's anchor to hope, representing what he believes humanity's future could be.
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