The Underground Labor Camp (地下王国) is a mine owned by the Teiai Corporation. They send people who are in debt with them here and pay them in perica for their hard work. In turn, debtors who seek freedom must earn enough perica to pay their debt back.
It is explained by Hyōdō to Ichijō during his dinner that it is actually a bunker to be used in case a war breaks out in the future. He would prefer to be the master of his own fate instead of letting the government decide his fate should a war breaks out.
Hyōdō describes it more akin to a massive vault, or an underground empire which would have stores, hospitals, golf courses, and casinos available only to those who are loyal to the Teiai Corporation when it is completed.
- In the live action film adaptation, the underground labor camp is located directly beneath the city.