Kumaso

About

Kumaso is the doctor of the "Upper World".

He is secretly planning a coup against Sumeragi, who mechanically controls this world, and is made of human brains connected together.

In the past he took part in an experiment at the order of Sumeragi. The subjects of the experiment were four orphaned sisters,
They are Z01, 02, 03, and 04, who grew up in a medical institution with Kumaso.
Kumaso treated the girls like family.
During the experiment, Z02, Z03, and Z04 are unable to withstand the load and die.
The surviving girl, Z01, becomes Kumaso's hope for the future of humanity.