I don't think any person in a suit can kill those aliens. If they provided Gantz for humanity and have access to the data in those black balls, it pretty much gives them power over every single one of them.
I think this manga is going to end up with a bunch of innards artistically splattered all over the floor.
Haha, thatīd be funny xD ...and really, really sad
BUT fitting for Gantz I guess!