I couldn't miss the chance to practice my drawing!
Players are sent into battle against Gilgamesh, who will do nothing against them. After 7 turns Gilgamesh will notify the player of how much total damage their party inflicted, then flee. The player has until then to deal as much damage to Gilgamesh as possible. The actual amount of damage is irrelevant, the player will receive full completion bonuses including Mastery - they simply earn bragging rights for dealing as much damage to Gilgamesh as they can.
There were two variants of the battle - the first was a Jump Start Battle where the player would begin with two Soul Break segments charged, but the Soul Break otherwise would not charge. The second was a "Broken Soul Battle" where the Soul Break gauge would not charge at all.