If you do Roger's Ancient Book Sidequest, you'll eventually uncover an item called the Rabbit Ears Chalice in the Ursa Lava Caves. With the item equipped, enter the code below during a battle to have that character blow up and deal damage to the enemy.

Code - Effect

Up, Up, Down, Down, Left, Right, Left, Right, (Circle X or X Circle, depends on refinement) - Character explodes and deals damage.