New Play Modes
Every time a character shouts out a voice clip in battle, it's saved onto your memory card. When you turn on your PlayStation, the game reads all files on the memory card and all the voice clips that have been heard in battle become "active" - you can listen to them again on the Voice Collection option on the start screen. However, you can do more than that!
When you get 30% (384) of the voice clips, a new option will open up when you start a new game, allowing you to choose Galaxy mode. This harder mode raises all monster stats, including speed and intelligence. When you get 50% (639) of the voice clips, you'll open Universe mode, which is even tougher!
When you get 75% (959) of the voice clips, you'll open up a Music Test mode on the Voice Collection screen. You can choose the clip to hear, or get a random one to play.
Many voice clips are tough to get. First off, the easier ones are the ones that play during Killer Moves; just do that Killer Move and the voice clip will play. Next are the ones that play during spells. Most spells have not one but two voice clips, the second one being very rare; I don't know for sure what affects which clip is played.
MaxAgond@aol.com claims that it makes a difference whether you actually choose the spell to be cast or if the AI casts it automatically. After that are the tough ones; just play through with every character as much as you can and most of them will eventually play out (e.g. when a character is wounded, dies, raises a level, wins a battle, etc.) The hardest ones to get are when another character dies. Your Emotional Level for that character must be high enough that you call out their name, but you usually can't have that kind of level for more than one character at a time. So don't expect to get all of those. ^^; But you definitely must play the game through at least twice to get all twelve characters; there's no chance otherwise.