The best explanation right now is having the will/ambition of being the strongest swordsmen. Since there's no haki inside a perm black blade there's no relation in mastery your haki, it's simply applies there by default in your journey of becoming the greatest (so by default if you want to be great you'll need to apply Mihawk's application that he explained to Zoro). Once the blade accepts you AND sees your ambition being "achieved" it seems like it simply converts the users ambition and haki to a perm black blade grade.
There really isn't much of a power up of upping the grade of your sword other then making the quality of the blade more harder/sturdier. Every cursed/high graded sword already had it's unique perks prior to turning it black.
This explains why other top tiers with blades haven't witnessed a perm black blade. They simply do not have the ambition to be the greatest swordsmen.
There really isn't much of a power up of upping the grade of your sword other then making the quality of the blade more harder/sturdier. Every cursed/high graded sword already had it's unique perks prior to turning it black.
This explains why other top tiers with blades haven't witnessed a perm black blade. They simply do not have the ambition to be the greatest swordsmen.