Enma is clearly special and not just as a training tool. Now it does also operate as a training tool as a side effect, but the sword itself allows the wielder to do things they couldn’t without it.
To the best I can tell it uses the wielder’s own Haki but it allows them access to more of their Haki than they would normally be able to produce without it.
I don’t understand why Zoro fans are so against Enma being a power up. It obviously is. It doesn’t make Zoro any lesser, in fact it’s still huge feat for him to be able to wield this sword that would likely kill a lesser swordsman for trying.
Zoro fans and Sanji fans are both in denial about Enma and the RS. If Enma wasn’t special it wouldn’t be hyped as the only sword to ever scar Kaido. And it’s crazy because it isn’t a knock on either of them yet people try to make it so.