The White Cube is a mysterious form of Underground technology that is capable of absorbing, containing, and disguising Mania. It has many possible uses, ranging from a potent method of anti-Mania treatment to a means of hiding from Mania-monitoring technology. It is powerful enough even to contain an awakened Inheritance, and an individual holding a White Cube is invisible even to the Observatorium. It is made of a crystalline material, and despite the name is an irregular polyhedron rather than a cube.
The White Cube also appears to be effective against the Rules, as the Chief was able to channel a blast of Rules through their Shackles into Corpus 002 without being harmed by it themself due to their possession of a cube.
Bai Yi and Che stole at least one White Cube (but likely more) when they escaped from the Underground. Their cubes were used by Zoya to seal the Inheritance in Syndicate, to heal the Chief from their coma induced by connection to BR-002, and in the final battle between the Chief and Corpus 002. Parma also used a Black Cube containing multiple inheritances to create BR-004; its usage seems consistent with the capabilities of a White Cube, but it is unclear what (if anything) the differences between them are.