oh...

[HUcast_Josh]

Today i was finishing of the human story and for some reason reve came along instead of Kai

How did that happen? anyone else had this?

[Inexx]

Reve never came with me til after i beat the game

[Evila]

Your choices during the storyline determine who shows up after the ending.
There's scenes with Sarisa, Kai, Ogi, Reve, and the Mayor.
Not sure how to trigger the Mayor one though.
I've been meaning to test it out and work on some other PSZ stuff but I am the master of wasting time.
Anyways, for the rest, there's an FAQ floating around, and the official strategy guide.

[EDIT] Oh oh oh I just realized you're probably talking about who joins you for that last mission. Reve joins if you're a Human player, and Kai joins if you're a Newman or Cast player. There's no way to change that, it's just how it always happens. Disregard the previous text. :wacko: