Gantz/Minus and Gantz/EXA

Hey guys,

I just now noticed that there is something called Gantz/EXA out there, and that it is considered cannon!

Do you guys have any info on this?
I know that Gantz/Minus occurs before Gantz, but is Gantz/EXA something that is supposed to occur at the same time as Gantz, or after?

Because, if it's occuring after Gantz, it might contain a lot of info on how Gantz will be ending!

For example (Gantz/EXA spoilers!):

Spoiler show

Kishimoto Kei is found in a Gantz ball and is alive!

I don't think Exa is relevant to the actual Gantz storyline. Oku was not even involved to that story. I rather see it as a fan story and the artwork was really wonky and offmodel...:/

Gantz exa: I know Oku has nothing to do with it, and Gantz minus is before Volume 1 of the "Gantz" series, and features Izumi and Nishi along with some other guy (main) and girl.