Katastrophe - After the Gantz game is finished, the Earth is invaded by giant aliens... During this arc, we get to know many more hunters, teams:
In chapter 329 Kurono and Reika invited Gantz hunters in Japan to join the Tokyo team and fight against the invading giant aliens, rescuing the captured civilians.
Zaibatsu big wigs : a group of Japanese businessmen who hacked some (7 seen) Gantz-balls, so they have full access to most of their funcions.