Hillo is a crossover of "Hi" and "Hello" also when your brain can't decide either to say "hi" or "hello" so you blurt out "HILLO" This often used with BFF's when they greet each other.
Bestie : Hi!
Me : Thinking "Say something you sleep deprived brainless idiot!
Me : HILLO
Bestie : Oooh~ that how we should greet each other from now on!
Me : Oooh~ YESH!!