To explain why Avion is on white robes first, it first needs to be explained that in the lower stadiums, the soldiers basically can do anything as long as it isn't illegal. That was why they're abusive and arrogant. There are very many things that one can do to prisoners that aren't illegal.
Like teasing or roasting them...
However, when Avion came, a mortal, it was hilarious to worship him. It's like making a dog a mayor or a kid a king. On top of that, he actually says nice stuff.
Therefore, when they learned Avion was placed in the most dangerous battle in the Rank Dih stadium ever in history, they planned something, something hilarious.
A ceremony before the Mortal Saint becomes a martyr. Avion couldn't laugh with them since the last step to becoming a martyr is dying.
