It doesn't lol. Enma already served its purpose. Zoro cut Kaido like Hiyori and Tengu said it should. Tengu never specified it turning black in Wano, just in the future. Ame also did it, and thats my point. It's not anymore special than Ame outside of being a cursed blade that siphons haki. Ame creates the other half of Kaido's scar.
Yeah, no... lol
Enma's hasn't served its purpose no matter which angle you look at it from.
If Enma's purpose is Oden's goal, then it hasn't achieved that yet.
If Enma's purpose is to destroy Kaido as Kawamatsu suggests when talking about swords in general, then it hasn't achieved that either.
If Enma's purpose is Zoro's goal of slicing Kaido into pieces, unachieved too.
I've got no clue what "Hiyori and Tengu" thing you're talking about.
They never suggest that Enma's purpose in this arc is to give Kaido a cut.
They never even talk about Enma's purpose in this arc.
My post about Wado has to do with be pure fact that it is the real sibling blade to Enma. They were both forged by Kozaburo, both tied to the Shimotsuki bloodline, which Zoro is seemingly related to, as was Ryuuma. Wado is Zoro's first sword, which he has been through more battles with it. Thematically it would work better because it's the 1 blade he's had since beginning.
Again, it doesn't matter if
Zoro has been through more battles with it.
Zoro doesn't need to recreate all of Oden's experiences with Enma for it to be black.
Enma ALREADY has that experience of battle, hence Zoro needs to do little with it for it to be forged black.