I wonder if it really is -63%total attack or something else, like
-63% weapon atk or
-63% atk from stats.
According to this topic High Guard does not really cut the total damage in half, like the tooltip description implies, but only reduces the base damage (the “physical damage” in your character stats). And that means skill damage will probably stay the same (equipment atk/weapon atk too?).
And my guess would be that it’ll be the same for Guardian: -18%~-63% status attack, but skill attack (and equip/weapon atk?) won’t be affected.
And even if you use High Guard and Guardian at the same time for >100% attack reduction, skill attack (and equip/weapon atk?) should stay the same.
I also wonder : Does High Guard reduce the “critical attack” stat, or just the base “physical attack” stat? If it doesn’t affect “critical attack” then high crit/high crit attack builds might be interesting


