I'm travel with my imagination, but it would be awesome if a Koi Devil Fruit user can transform into a Dragon if he climbs Wano's fall similiar to the Japanese mythology. This could explain Kaido's immense strenght, cause devil fruit users became much weaker under the water and if the Koi user can climb the entire fall nonetheless, he should acquire an immense strenght to do that. Also this could explain why is the strongest creature in the see too.