Apparently the cast from Disagea are recruitable once you satisfy certain criterion. http://phantom-kingdom.com/kakushi.html
The link above is for a contest on guessing who are the hidden characters in this game. From what I have read so far, this game is as freaking hilarious as Disagea.
On a similar note, has anyone seen the following images?
I thought the second one where Laharl is wearing the costume of Ash and Prinny as Putties is pretty funny.