Parry blue-flash attacks, dodge red-flash attacks, and avoid black-flash attacks entirely. A perfect answer to a brutal or killer move triggers ghostep, which puts Soul behind the attacker.
Phantom Blade Zero gives you three defensive answers and punishes you for using the wrong one. Block absorbs damage, parry damages the enemy's posture, dodge avoids the hit entirely. Which one you need is decided by the colour of the attack, not by the animation.
Learn the colours and the game becomes readable. Learn the animations and you will spend the first boss fight guessing.
The three answers
Answer
What it does
Sha-chi cost
When it is correct
Block
Stops health damage, keeps you in place
Small per hit, heavy against brutal moves
Chip damage you cannot read yet
Parry
Deflects, drains enemy posture, enables ghostep
None on success
Blue-flash attacks
Dodge
Moves you out of the hitbox
None
Red-flash attacks, area attacks, repositioning
Blocking is the training wheel, not the strategy. It costs sha-chi every time it absorbs something, and the resource you are spending is the same one that pays for your heavy attacks. A player who blocks through a combo has nothing left to punish with.
The colour tells
Blue flash means parry. Red flash means dodge. Black flash means neither: those attacks cannot be blocked or parried, and the only answer is to be somewhere else.
The game separates the dangerous moves into two families. Brutal moves are the ones that wreck your sha-chi if you block them. Killer moves are the ones that ignore block and parry entirely. Both are telegraphed, and both are answered by timing rather than by holding a button.
:: warning The most common death in the first ten hours is a red-flash attack met with a parry. The input looks like it worked because Soul raises his blade; the hit still lands.