Z-City

Z-City (Z市, Z Shi) is a large city within the world of OnePunch-Man. It consists of a business district, a residential district, and an abandoned, trashed and deserted area. Saitama and Genos are inhabitants of the latter area, which is home to many Mysterious Being's, but has cheap rent. Along with several other superheroes, they defend the city from the many monsters spawning in it.

Shelter Nr. 7
Shelter Nr. 7 is a public shelter located in Z-City, built by the Hero Association in the event of attack an by Mysterious Beings. Externally, it consists of a giant dome lined with circular vents, which is able to withstand anything from extreme temperatures to missile attacks.

Shelter Nr. 7 very much resembles a sporting venue, with at least seven different entrances meant to accommodate large crowds. It was designed specifically to repel Mysterious Beings, and features biometric authenticators at each entrance to detect any possibly masquerading as human; once the shelter's defense system is active, all entrances are sealed and locked.

The interior of the shelter is largely open space, with rafters overhead installed with sprinklers and speakers to spray negative ions and play classical music, respectively—both meant to calm its likely-panicking evacuees.

However, Shelter Nr. 7 does not feature any restrooms, a rather glaring oversight given its enormous capacity.

Superheroes

 * Saitama
 * Genos
 * License-less Rider

Monsters

 * Crabrante (Deceased)
 * Underground People
 * Underground King (Deceased)
 * Kombu Infinity
 * Personification Of A Light Pull Cord (Deceased)
 * Super Custom YO649Z Mk. II (Deceased)
 * Hotdog (Deceased)
 * Fish of Darkness

Saitama Introduction Arc
The Underground King leads his forces to invade the overworld, but is killed soon after surfacing.

House of Evolution Arc
Z-City is first mentioned by name when there is a mosquito outbreak caused by Mosquito Girl. Genos ends fighting Mosquito Girl, but is ultimately defeated after Mosquito Girl transforms. Mosquito Girl is then killed by Saitama.

Rumored Monster Arc
The Hero Association begins an investigation of Z-City especially the uninhabited parts and sends Golden Ball and Spring Mustache to investigate. They do not find the rumored monster, but instead find Kombu Infinity. The A-Classes heroes are defeated, but not before they call back up. Saitama then appears after shopping and beats up Kombu Infinity.

Giant Meteor Arc
A Giant Meteor is heading straight towards Z-City and Genos and Bang are assigned to take care of it.