The whole Ryuma and Zoro story. No one still believe Zoro.
I expect something, why Oda want so badly Zoro going to Ryuma grave, what gonna happen if he goes their? Would something change, I mean the wano samurai, Hiyori and co don´t would believe him.
Now something come in my mind, Oda loves Star wars and we know the ghost of the master come back sometimes, what if when Zoro arrive at the Grave, Ryuma ghost shows up and tell about his story and that Zoro defeat him(at least his Zombie version).
Kawamatsu and co would see that and would believe Zoro words, which means he don´t speak lies.
I can see something like this, we are after all in Wano where Japanese mythology play a big part.^^