The Zimvoid is the name given to an extra-dimensional planetoid that appears in several issues of the comic series.
In Issue 46, both Zim and Dib detect an Irken distress signal coming from Pandora's Quadrangle and go to investigate it. Arriving at the signal's location, their ships are sucked through a portal and find themselves deposited over a small planet surrounded by such portals and with a massive tower-like machine in its center. Their ships malfunction, presumably as an effect of the tower, and crash among piles of other Voot Runners. Zim is then captured by the planet's inhabitants, who wear bug-like armor, while Dib and GIR escape into some underground caves and find an entire city full of copies of Zim.
Issue 47 opens with Zim's captors (more copies of himself) explaining that the portals surrounding the planet, which are created by the failed superweapon in its middle, each lead to a different alternate universe. All the Zims present in the Zimvoid (as they've dubbed the location) each followed the distress signal into their respective version of the Quadrangle, and ended up stranded on the planet. Unable to leave, they've since established a strict hierarchy, with each Zim numbered and assigned a job according to that number, with Zim Number 1 ruling over all of them from the tower with his 100 elites, the useful Zims allowed to live in the walled city at its base, and all the rejects forced to live in the caves.
Meanwhile, Dib learns all of this as well when he meets the Zim Resistance, a group of renegade Zims who refuse to abide by the hierarchy, both due to how repressive it is and because they each all think they should be Number 1. Their leader, the Elder, has a plan to recruit aid from the Zim gladiators fighting in the arena for the right to move up the ranks, and with Dib and GIR's help they break into the arena just as Zim (who has been fighting his counterparts for a better role) is about to fight Zim 100 for the right to join Number 1's elite.
In Issue 48, Dib's interference inadvertently allows his Zim to beat Zim 100, as he accidentally talks 100 into knocking himself out while trying to convince him to join the Resistance. This allows Zim to take his place as a member of the elite, and he's taken to the tower. There, he's informed by Zim Number 2 on why Number 1 is the greatest Zim, and how all the elites train rigorously to become just as good as him; in exchange, once they're done training, Number 1 gives them restored Voots and improved weapons, and then sends them back through the portals to conquer their own Earths.
At the same time, Zim 100 informs the Resistance and the other arena Zims about all this. Infuriated at the revelation that Number 1 could have sent them all home at any time, the other gladiators join the Resistance, which then storms Number 1's tower. After the resulting battle, most of the Zims on both sides are knocked out, with the remaining rebels (Dib, GIR, Zim 2000, and Zim 2002) being captured by Zim and Zim Number 2; the latter keeps guard on the unconscious members, while the former takes the others before Number 1. And to everyone's shock, Number 1 reveals that he's actually a robotic suit containing an alternate Dib.
This other Dib, whom GIR dubs "Zib" due to having an Irken PAK on the back of his head, reveals that after he defeated the Irken Empire in his own reality and discovered the secret of Pandora's Quadrangle, he created the signal and lured all the Zims to the void with the intent of using them to destroy the Irkens in all other timelines as well. The hierarchy was designed to weed out the weaker Zims, while the Elite's training was meant to make them easier to control (and because it was funny to hurt them). Now, he's developed a "Dib virus" that will control them completely and use them to spread to the Irken Armadas of other timelines and destroy them.
Zib then has Number 2, who has been given the virus and is fully brainwashed, lock up the other Zims, while he promises Dib that his timeline will be the first one to have its Irkens destroyed. However, he also assigns Dib janitorial duties, seeing him as incompetent due to being the only Dib who also followed the signal into the void. Dib is despondent at his counterpart's seeming superiority and success, but soon discovers to his horror that the Zimvoid isn't another dimension but Zib's home timeline.
When confronted with this, Zib admits that his attempt to destroy the Irkens backfired and destroyed his entire reality except him and his castle, creating the Quadrangle portals in the process. Despite this, he is still determined to repeat his attempts on the Irkens in every timeline, being perfectly willing to risk destroying more realities in doing so, justifying it with the fact that there are infinite universes.
Before he can carry this out on Dib's timeline, however, the Resistance - whom Dib had freed before confronting Zib - attack Zib with their upgraded Voots. He fights back with a mech designed in his appearance, and quickly gains the upper hand. But before he can win, our Zim hijacks his anti-Irken weapon and the portals, using them to alter the pasts of the other Zims and make them identical to his own; despite Dib pointing out that this isn't how timelines work, everyone is sent back to their own realities.
After this, the portals are sealed, leaving Zib trapped alone in the now empty void.
Facts of Doom
- The story arc in which the Zimvoid appears (Issues 46 to 49) is dubbed "Battle Void". Presumably this was to keep secret Issue 46's twist ending that it's full of copies of Zim.
- Oddly, GIR functions fine in the Zimvoid despite all the Zims saying that their GIRs don't work there. It is possbile it had something to do with GIR being with Dib when they entered the Zimvoid.
- One of the Zims in the Zimvoid resembles a space bee seen in Invader Zim: Enter the Florpus.
- According to the Elder, the Zims only just started arriving in the Zimvoid six months before the story's present.