Number 128 starts the battle with Net, which inflicts Stop on a party member, and it uses it randomly throughout the rest of the battle. It counters physical attacks with Blood Feast, a physical attack that acts like the Drain spell, restoring some of its HP. If its Right and Left Blades are destroyed, Number 128 will use Gale Cut, a Wind-elemental attack that hits the entire party. If either blade is killed it will regenerate, so it is best to ignore them and focus on Number 128.
If the battle goes on for too long (usually when the player continuously attempts to steal the Kazekiri), Number 128 may use Blaster on the party, attempting to inflict Death to all characters and resulting in a Game Over if it's successful.