two things here, one is a history change, and the other is a fluff charecter trait.
Void is a navi made by a net 'gang' called "the demons of the abyss", which is really a bunch of geeks who are into the paranormal. He was given to Damian when he was a kid to make their game more interesting against the "defenders of light". basically the only rule of the game is to make navi's and seed them amongst other netOps for the sole reason to have them battle till one 'gangs' server crashes, which are respectively "the abyss" and "heaven's gate". The game is monitored by the imp/cherib program, which is a small prog like program that follows their assigned navi and gives them orders and upgrades, and relays their success and failures. these smaller programs cannot be seen by other netOps and navis outside of the game. all the programs suffer from some level of delusion from their years spent in the game, but due to a blow to the head by a hands, Void is pretty out of it. all of the abyssal's navi designs are based on some monster, and all of the defenders are based on protective spirits.
and the fluff:
Void, being shadow, has the ability to change his form easily, though he still looks like he always does with yellow eyes and being made of shadows. he also can't really change in size without messing with his density, so if tries to grow too large he'll just wisp away, and he can't go too small cause of pressure
I hope this is ok