Does Zoro have a legitimate claim to wield Shusui? It was given to him by Ryuma, but at the time he was powered by Brook’s Shadow.
The zombies inherit the combat abilities and personalities of the shadows put in them, but the bodies are just empty vessels they have no recollection of their past lives. So then Ryuma himself never gave Shusui to Zoro, and it was technically given to him by Brook.
So while Zoro may not have stolen Shusui, a national treasure to Wano, like many of the people around Wano are suggesting, he technically isn’t the rightful owner of it either.
I suspect that Shusui will play a role in defeating Kaido, since they keep stressing over and over that Ryuma once took down a dragon with it.
And I think Zoro will earn the right to wield Shusui during this arc, thus the reason for him losing the sword at the beginning of the arc.
At the end of the Wano arc Momonosuke could gift it to him for helping to save the country.
*Theory by OUwere2112