I just re-read all the chapters since Kei has died.
I recommend EVERYONE to do this, shit will make so much more sense.
Its amazing really, in Gantz time its only been a few hours since Kei died. After Kei died, Vamps got teleported to the Gantz base, soon after they got teleported to Osaka and they've been running around there since.
I mean, even the Osaka woman, she's only know Kurono for a few hours yet she said she loved him. And the thing she said about having a son? She actually mentioned it when she first met Kato.
So yeah, I've rediscovered my liking for Gantz because really everything has happened in quick succession so by rereading it all, it will make much more sense.