After playing through both PSII and PSIV I always liked the aspect that both Eusis and Chaz both got Megid. On the other hand I didn't enjoy that Megid did damage back to your party members when Eusis used it.
Mainly I always figured that the difference between Eusis' Megid and Chaz's Megid was due to the fact that maybe Eusis couldn't get over Nei's death thus his anger caused the technique to backfire, while Chaz had come to terms with his anger and sadness after his battle with Re-Fazes illusion thus the power of Megid couldn't backfire and would actually deal its true damage to his foes. What do you think?