- 'He can understand now why the Anti-Gem drives him to destroy the Gem: however many potential Chosen Ones there are in the universe, they are grossly outnumbered by average shmucks to whom the Gem would only grant powers of destruction.'
First appearing Plans Within Plans, the Anti-Gem is an arcane artifact that is essentially an opposite version of The Gem. It is the only known object in the universe capable of completely neutralizing the Gem's power.
According to Rocket, the Anti-Gem was found by taillesskangaru while he was out treasure-hunting on the planet Wetickra. Rocket, having met taillesskangaru just before he "disappeared", somehow came to possess the artifact. It is described as a "twin" of the infamous Gem, even though it is very small compared to the Gem (the Anti-Gem can fit inside a coat pocket, while the Gem takes up the space of a large cave. It is the only object in the universe which can nullify the power of the Gem should it be released (either through the Chosen Ones or by some other means) and essentially the only object which can destroy the Gem.
It is implied that the Gem and Anti-Gem were once held together. It is said that should anyone come into contact with the Anti-Gem, the chemical properties of the Anti-Gem will drive that person to relentlessly seek the Gem and unite it with the Anti-Gem, causing the destruction of both. This Rocket managed to force Hannibal Barca to do. But rather than drive Hannibal into tunnel-visioned obsession as Rocket had hoped, the artifact motivated him to action without impeding his logical capacity. Hannibal proceeded to cover his bases with a trip to Arrakis with the aim of learning as much as he could about the situation from the Padishah Emperor.