Btw what do think black blades do besides durability, because if that’s their only thing you know the community will meme on them
I was slowly less interested in the concept chapter after chapter. Wano pretty much gave us zero clues about it which is weird. We only got to know that there are no "Cursed" swords.
If I have to be 100% honest with you, I believe even Oda himself doesn't know what to do with this and he will just come up with something on a whim.
It makes the sword indestructible and aside from that I doubt it means anything, grade improvement maybe? W/e.
Oda gradually killed swordsmanship in the manga. I developed a liking for this style because it felt important and amazing. Now it's just a form of fighting/channeling your Haki.
Oh, and of course
LEATHALITY.