A concept first introduced by Luke Skywalker, the anti-Force was the name given to the arcane energy field that connected Waru's universe, standing in stark contrast to the Force as it was understood in the primary universe. While isolated from his home dimension aboard Crseih Station, Waru found that the only way to gather sufficient power to return to his own reality was to counteract the Force of the universe holding him prisoner with the anti-Force from his own; this he accomplished by siphoning the life energies of numerous sentient individuals who encountered him during a journey undertaken to cure them of diverse illnesses.
It is possible the anti-Force existed within the pocket dimension called otherspace. A rumor circulating within the galaxy suggested that Cronal, a former Prophet of the Dark Side, gained entry to otherspace and exploited the anti-Force to enable his resurrection.