Osaka Arc: where is Nishi?
Lots of you are asking this.
I think that the general board wide view is that he is hiding and waiting for a chance to nab some high point kills. I think there is a little more too it though.
I think we can all agree that Nishi knows more about what is going on in gantz than any gantzer on the Tokyo team. I think he may realise that this mission is over his head and that is why he is staying the hell out of the way and has decided not to reveal himself to the Tokyo or Osaka team.
I also remember he currently has 0 points. He has no points to lose if the mission goes bust so why should he stick his neck out?