Hey dudes, this is my first Post on this homepage and possibly my English is not to well which means i maybe should not open threads with themes which are probably already discussed 1 gogolplex times, but, however, I will.
Early on in this Manga, the reader asks himself: what is the purpose of gantz?
Another big question is whether gantz is a good guy or the bastard we know.
After the latest spoilers of (chapter 280) something popped into my mind, making me very confident about gantz being a good guy.
So before reading that, in chapter 280 will be a big story twist, and if you don't want to get spoiled, you should not read on.
The reason of my guess is that gantz IS actually trying to get the best possible team for Katastrophe, or maybe for even later, and Nishi is doing the same thing (or at least he was).
What is the first thing people want to do in Gantz?
They want to run away, they want to go home.
We thought gantz is just some cruel asshole who forces the humans to fight, but if we consider the information we got in 280, it is a necessary thing to prevent the soldiers from running away.
The first two missions looked like training missions, the Aliens were not strong and had no move like the buddha or the nuri laser.
They probably were to sort out the good ones.
Now remember what Nishi does:
He helps Kurono, he is seeing, after many missions as sole survivor, there may be one ally who is actually worth helping and supporting to get a team together, former or later.
The second thing gantz players usually want are bying their freedom which should take at least 4-5 Missions for a rookie (at least for the Missions we saw), preventing them from leaving and forcing them to get stronger.
Without a good usage of the suit and the weapons, you are fucked in Gantz (cept if your name is Inaba.....)
After you came to this point, you will either be a paranoid bastard who enjoys being in gantz, getting the stronger weapon, or you will have lost allys and friends you desire to reborn, or you can't leave for your team's sake.
Ofc Kurono was a exception here, but exceptions are proving the rule.
And remember, both, Kurono and Izumi came back.
So to the point of KATASTROPHE (i like to caps it :P) gantz and Nishi tried to get a team running.
Nishi knew, the 'scums' dying in their first mission are not worth helping, he needed many people (so many had to die to get new flesh into the room) to search after the decent fighters.
The Point system is actually a way to motivate the gantzers to get stronger, to fight of the alien invasion or whatever katastrophe means.
Because of that gantz did not need the time limit anymore, he know the gantzers had no other choice than to fight, before, in my opinion, it was to prevent them from hiding out or running away forever.
I have a feeling the invisibility plays a role in this too, but i cannot figure it out yet.
Now more about Nishis role of Gantza's little helper:
Nishi must be pretty sure about the productive purpose of gantz because he defends gantz.
When host Samurai wanted to attack gantz, nishi targeted him.
We don't know whether Gantz is invincible or not, but why should Nishi do such a thing?
Nishis turns out more and more like an antihero, who, although being a coldless, misanthropic killer, wants to save the world and knows gantz is their only chance to do so.
In 280, he laughed about the little problems of the other gantzers, means he had to know about the Katastrophe all the time and wants to prevent it (else it would not be a 'problem' for him).
Now, let's look at the Izumi-Nishi train szene.
There was something which wondered me.
Izumi said, he wants to show the world how 'superior' japan is.
Does it means KATASTROPHE is something like a tourney?
If it was just a worldwide alien invasion, there was no superior and inferior, there was just alien slaying deluxe.
So now we come to the things speaking against my theory:
From Nishi's ppoint it seems to be about surviving and nuclear war (though he said he wants to go to american/german/israelian team which would speak for the toruney theory), from Izumis it's something to compete in and win, like sports.
Also, Nishi (if we assume the translation was correct) wanted to leave gantz.
How could he do so if he knows there are just some rookies worms and the end is near?
Have fun posting to this, i have some other clues, but atm i have to go