The Void is, as the name states, an empty space. Before The Second Coming's appearance in this place, there is nothing to be seen. After he came though, the area became full with lines and shapes used during the battle against the 4D-Hyper Diamond.
In the episode, the void is seen having nothing. Then a dot appears, which then later turns into a line and The Second Coming gets up from that thin line. From there, The Second Coming discovered a character appears to be Phi, they both made friendship later. They both later discovered an attacking character appears to be a "4D-Hyper Diamond", it attacks everything in order to attack The Second Coming and Phi. After geometry things, Phi sacrificed itself to destroy the hyper diamond After that, The Second Coming discovers an area featuring something known as "fractals". From there, The Second Coming discovers another stick figure with his color, seems to be his other self, wearing a cowboy hat, referencing Animation vs. Physics.
