Question about Zantei

I was wondering abt the damage output of zantei for my katana. It continuously hits 5k damage per hit, but i've seen people doing much higher damage with their last hit tha their first three. So i was wondering if im doing something wrong that is perhaps screwing up the skill damage. Or maybe its because of my gear?
In any case i need some guidance here thanks!

 

Zantei works as a counter, if you receive a hit on the first 3 slash you will nullify the damage to 0 and proceeds to deal a counter slash that deals huge damage+armor break (50%defense reduction).

Hasso happa have decent damage ans could be used actively instead of as a counter.

In short, use them both
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