Cave of Evil
The Cave of Evil (ケイヴ・オヴ・イヴル, keivu ovu īvuru) is a nightclub located in the Harajuku district of Tokyo. Miho has some connection to it, but exactly what that is is still up for discussion. The predominant theories are that: Miho owns it (difficult to resolve since, by all appearances she is no older than eighteen); that Miho's parents own the place; or that Miho was "taken-in" by employees there after some major life event (generally either her parents' death/leaving, or the Endgames collapse).
The Cave of Evil first appeared when Largo managed to find himself a "cave of evil" (note the lower case) and discovered the Necrowombicon and Miho. Upon Largo's imminent return, we saw that it was in fact a dance club, and Largo saw that it contained zombies. Around this time Miho gave Kimiko a free pass to the club, which confused everyone involved.
Later, in Chapter 6, Ping told Piro that the two of them had been given free passes by Miho, and that she wanted them to come that night. After some additional angst involving Kimiko's phone number, they went, and Piro attempted to listen to the Mumu-chan's Voicevoice Paradise radio show, which had Kimiko on as a guest.
Employees
Known employees of the Cave of Evil include Kenji, a DJ with an office and audio equipment, so he might be more, Waltah, a bartender if not more, and Komugiko, a (cosplaying ?) foxgirl. Miho has some connection, too, but whether as an employee is uncertain.