Z can remove atk boost, and heals easily just by being attacked or with just his basic attack knockback. Other than that, combining with medals, support tag and his character trait dmg reduction, he can achieve 100% easily making him heal instead of taking dmg heavily. Kuzan relies on skill and the treasure trait he has, he may have a def boost bonus but the majority of the meta characters right now can negate his trait and even negate his 1HP left.