SPOILERS, I think

Okay, I was always dubious on Lionheart being a "main character".
I mean, think about it: he disappears RIGHT at the beginning of the game, and then he just randomly rejoins the team at the VERY END of the game.
You don't even SEE him during the game until that last part (alright, maybe once, but that part barely counts).
He's gone for the whole game, and then he decides to stick with you when you're about to enter the final dungeon.

If this is a "main character", then I'm Santa Claus.
A main character should at least take some kind of part in the game itself other than the final dungeon.

To me, Lionheart is just another "fourth character", but a fourth character that never switches with another character.