Wouldn't Kei want to get back at them for killing his brother or something?
His family was fucked up, remember? He didn't really care for anybody, except for Tai, later.
Family is family no matter how fcked up they are...but yeah maybe not revenge.
Well the thing is there is allot of plot holes just got to ignore them hehe
Look at Italy they got destroyed there and the aliens that invaded them are nothing compared to them in fact the bugs or what ever on the ship was more of a challenge than the major aliens as well
After 37 volumes, the ending is the way we wanted, it is rare to find something else after the last battle, i mean, since the start Kurono is the hero, and we wanted this ending through the entire story. Happy ending everybody ^^
I thought the ending was sufficient, The explanation in Chapters 370-372, Oku's quality of writing quite impressed me. At the end of it all, Gantz is left with quite a lot of characters which of whom storys were not completely realised and or rushed. But its a better ending than any of Oku's previous works.