Quick Bullet

Quick Bullet is an Enchanted Soul in Castlevania: Dawn of Sorrow you receive by killing the Dead Warrior. It is similar to Quick Parry in Castlevania: Aria of Sorrow as it allows you to interrupt your attack and witch to your equipped bullet soul.

This is usually only useful for slow weapons and it doesn't work on Throwing Weapon. Note also that certain souls like Blood Sucker interrupt the attack but don't follow up with their own.