He's vaguely mentioned by aqua dolphin when explaining how judai retains his power, it's later stated he's a force of the universe and as such was there since the very start
Darkness also knows of the numeron code, Something that could only be true if he was born since the beginning of time
It's also portrayed that darkness is composed,cold and calculated. Haou is portrayed in the dame manner and he's the vessel for the gentle darkness so it's fair to say they should have commonalities if they are the same being which they do
