Now that I've finished the game, I've been looking into which of the character is the most broken (a Tales tradition after all)
Elise wins as she cannot be killed.
The only thing that can go through your guard are some weird arts (like Soaring Vortex) or Mystic Arts which you will laugh at because most of them are elemental and they'll be mostly or fully negated by your 100 resistance to every element. While you are blocking, you reflect damage and toss Pow Hammers and recover HP.
Decreases damage received while guarding to 1
Doubles damage received if not guarding
Prevents being knocked out while guarding
Guard cannot be broken
10% chance to strike with a Pow Hammer upon receiving damage
Reflects 20% of damage received while guarding
Recovers HP gradually while guarding
15% chance to recover HP upon receiving damage
40% chance to automatically revive after being knocked out (once per battle)
100% chance to automatically revive after being knocked out (once per battle)