Zhou saw the blade disappear, but there would be little he could do in response to it.  The entire scene was too close, and he wasn't about to take any steps back simply because he was going to be hurt.  However, he also knew that they weren't real petals, but slivers of the blade.  Metal.  Metal could be handled in a variety of different ways.  His reiatsu spiked as his blade and he unified for a moment, and electricity would supercharge the air around him.  A strong enough electrical charge would be utilized to strike at each of those petals as they came his way, ensuring that the attack, if it struck him, would be highly diminished.