One Piece Chapter 921 is recently out and it was one of the best chapters so far. This chapter showed Mythical Zoan-class Devil Fruit of Kaido that allows him to transform into a Chinese dragon. In this form, he is able to fly & dark clouds fill the sky upon his entrance. The theory of Kaido being a Dragon has been confirmed in OP chapter 921. Kaido looks quite dangerous in this form. What if Beast Kaido isn’t an Oni-Oni or human who ate the dragon Devil Fruit but is a real dragon from the past.
Original Devil Fruit Of Kaido Revealed: Legendary Beast
Kaido has never been named human but simply “creature” or “thing”. What if Kaido has been taken by the World Government a long time ago and they have been doing tests on him. It is assumed that some dragons are immortal so they could do whatever they desired and he wouldn’t die. Particularly Vegapunk used to work on these experiments and could obtain his DNA to form the artificial Dragon Devil Fruit (Momonosuke’s Devil Fruit).
Also, other dragons could be cloned from him but they seemed a little unusual than Kaido. Many times Kaido could escape but got caught from time to time and had to cut free again.
Some dragons have the ability to turn human to be able to cover. Since Kaido is a large dragon he also is large as a human person. It also would perform sense why Kaido is the most formidable creature on land, sea & in the sky. Since he is a dragon and not a Devil Fruit user he won’t die or suffer his strengths in water.
The research the World Government has been performing on him made him mad and he simply wants to forget everything and disappear. Whitebeard was the only person to challenge him and being able to equally face him. We don’t know how Shanks could prevent him from striking Whitebeard before Marineford war, so we can’t say for certain if Shanks is viewed to be strong enough by Kaido. Also, Kaido was assembling Devil Fruit users for his team. He wants to destroy the complete world because he doesn’t view any other solution to die.