I have a hypothesis about Kaido’s past and about his son.
I believe that Kaido is a dragon that consumed the Human Human Fruit, Model: Oni for several reasons.
- The existence of the artificial Dragon Devil Fruit
We know for a fact that Caesar Clown stole the research of the artificial Devil Fruits from Dr. Vegapunk and continued his research on Punk Hazard. From the several SMILEs shown throughout the Wano arc, we can summarize that the SMILEs are all essentially obtained using the essence or genes of the respective animal. However, in the case of the artificial Dragon Fruit created by Vegapunk, it presents a problem: there are no dragons currently alive in the One Piece world. So, for it to exist, a specimen dragon must have been available to Vegapunk, which I believe is Kaido himself during the time he was captured by the Marines.
- Kaido’s fixation on animal SMILEs and dinosaur Mythical Zoan users.
- Kaido’s invulnerability and incredible vitality in his Dragon form as well as his Oni form.
My theory is that Kaido was born into a family of dragons and lost his parents at a young age. Subsequently, he ate the Human Human Fruit, Model: Oni. In his younger years, Kaido had a smaller stature in his Oni form and was able to live amongst humans. However, he couldn’t feel a sense of belonging amongst humans due to his unnatural strength and vitality and for it, he was ostracized. He desperately longed for a place where he would belong. At some point, he met the Rocks Pirates. He felt that by being a pirate, he wouldn’t have to hide anymore and he would be accepted by the whole crew. He felt by doing so, he could finally have a purpose and reason to live and fight. He joined the crew as an apprentice pirate.
During the God Valley incident, Kaido recovered a dragon egg worshipped by the Celestial Dragons. It was the last of the dragons left in the One Piece world. Kaido considered the egg as the last living relation he had in this world and decided to call it his son. After the fall of Rocks D. Xebec, the various strong pirates on the crew left to make their own crews and conquer the Grand Line. Kaido decided to make his own crew consisting of animal Zoan users, just like how Fishmen crews consist only of Fishmen and Merfolk.
Eventually, Kaido found out that Roger also had a dragon egg aboard the Oro Jackson and decided to obtain it from Roger. He began to strengthen his crew. After taking over Wano, he found out that Roger had discovered Laugh Tale and disbanded his crew. The whereabouts of the egg were unknown. Kaido presumed it to be at Laugh Tale and decided to find Laugh Tale.
Following Roger’s death and subsequently Oden’s death, Kaido continued to rule over Wano amassing power and powerful Zoan fruits. The egg finally hatched after a few months but the child was too weak to survive and died within a few days. Kaido was crestfallen and decided to ask Big Mom for help. He felt that she would be able to revive him with the help of her Devil Fruit. By asking Big Mom for help, Kaido incurred a debt of a lifetime. Big Mom, however, was unable to save Kaido’s son.
Kaido lost the only kin he had left in the world and thus, was once again alone in this world. He lost his will to live for he had no reason to continue to live on. He found relief in sake and eventually, became a heavy drinker. He became suicidal and tried to kill himself in numerous ways. He even fought battles he had no chances of winning, for fighting took his mind off all the pain and trauma. Even though he was captured several times, he survived countless executions and torture. Through his many battles, he grew stronger. His desire to reach Laugh Tale in order to obtain the final dragon egg was the only reason he kept building up his strength and his crew.
At some point he met a user of the Dragon Mythical Zoan Devil Fruit and decided to make him the Ace of his crew and his son. Kaido’s son got captured by the Marines and was imprisoned at Impel Down. Kaido tried to save him all by himself and got captured. At some point, Vegapunk experimented on him and realised he was in fact a dragon and thus, used his genes to manufacture an artificial fruit, which was later consumed by Momonosuke.
During the Impel Down break-in by Blackbeard, he recruited the strongest from Level 6. In the mass breakout, Kaido’s son escaped and made it back.
Kaido wishes to meet with the samurai from the future in order to obtain information about Oden’s diary, so that he could find the remaining Poneglyphs and make it to Laugh Tale and find the last dragon egg.
*Theory by bronz_the_theorist