@PizzaBread already answered you guys:
Kaido saw Oden's Ryuo in the Scabbards as well. Beyond that, he fought Oden using Enma. Every sword has its own unique aura, and if Enma is one of only two blades to give Kaido his lone scar, it's no surprise that Kaido would remember it.
Man, I don't understand the fuss over Kaido recalling the last wielder of Enma. People recall Shanks/Roger when they see Luffy's Strawhat all the time. I don't understand how people are suddenly trying to distort this into some kind of powerscaling statement.
- Enma stored Oden's haki.
- Enma has special secret powers.
Both of the above conclusions are unwarranted from Kaido remembering the previous wielder of Enma when he is attacked with the blade. The same way people being reminded of Shanks/Roger in Luffy is no powerscaling statement.
The level of jumping to conclusions and general insanity going on here is apalling. You don't need to torture a scene of Kaido recalling the last wielder of a weapon to push your agenda regarding Enma being a power up or Kaido hurting Zoro only due to Enma. I've said that I think Enma is a power up, but it's sure as hell not because Kaido was reminded of Oden when Zoro attacked him with Enma.