We are timeless, bound as one, we cannot be silenced, as our song lingers on.
Apart from some sort of ninja mod which lets you become invisible to the game and invincible I can only speculate.
I have a theory that he is supposed to be in a different game but is somehow playing in another one so the game has trouble recognising him thus he's invincible and invisible.
He is registered in another game but is not there, very interesting.