Imaginary Cube is a nonexistent cube that can be found in Multiverse / The Outside, which makes a kind of Imaginary Polyhedrons. Unlike other Imaginary Polyhedrons, it can have any size, due to the nature of Imaginary Energy.
Imaginary Cubes are neutrally formed by dense Imaginary Energies, which will become interuniversal-kind because forces are transferable at that density. They will become primordial clouds at first, and then slowly transform into a rounded cube. However, it cannot be formed with really dense Imaginary Energies, due to being dangerous to universes.
If a primordial cloud is close to Imaginary Cube, then it will be submerged, allowing for better interuniversal expansion. Imaginary Energy can be transferred into Imaginary Polyhedrons, by Imaginarium Wire, which is why it is a primordial tier for stepping up from Universe Clusters.
Imaginary Cubes can be transformed into infrastructures, if one civilization masters the safety of Imaginary Cubes, as some Interuniversal metals can block Imaginary Energies. It can be anything, regardless of creativity, like alloy factories, energy cells, network hubs (with Imaginary Octahedrons), and Nexus Cubes (interuniversal transportation), although the mechanic won't change at all.
Alloying Interuniversal metals are often used in Imaginary Cubes, because it is a pataphysical object, which uses physics from universes.
Primordial Cubes are found in the Outside, and were equivalent to Imaginary Dodecahedrons during the very early Omniverse age. As the laws change over time, they start to diffuse into nothing but nonexistence. Normal Imaginary Cubes survive, and now resides midway to the Outside.