1-As one of the Yonko, Kaido is among the four strongest pirates alive, renowned as the “Strongest Creature in the World”. He attempted to take Whitebeard’s life, something few would dare, and subsequently clashed with Shanks. When Gekko Moriah was in his prime, Kaido fought him and emerged victorious, having killed his entire crew.
2-Not much is known about his earlier life, but sometime when he became a pirate, he had been defeated seven times and was captured eighteen times by the Marines and the other Yonko, causing him to live as a criminal. During those captures, Kaido was repeatedly tortured and given the death sentence forty times. However, no execution device was effective on him, and Kaido managed to sink nine massive prison ships.
3– Decades ago before the formation of his own crew, Kaido was part of the legendary Rocks Pirates as an apprentice. He was not recognized as one of the top pirates in the world until around the time when Gol D. Roger was executed. Notably, Kaido has a bounty of 4,611,100,000 Berries, which is the highest of any pirate currently alive, surpassed only by the bounties of the late Whitebeard and Gol D. Roger.
4-As with Charlotte Linlin, Kaido’s silhouette from Monkey D. Garp’s explanation greatly differs from when he made his first appearance. He was originally portrayed as having a wide face, a pointy beak-like nose, and a sinister grin when shown in the silhouette. However, Kaido’s final design featured some continuity with the original, as he retains a similar shaped nose and brow upon his reveal.
5-Kaido’s name may be based on the Japanese liquor, kaidou (海童).
6-Kaido’s epithet, Hyakujū (百獣), literally translates to “Hundred Beasts”. However, in Japanese, its meaning is somewhat closer to something along the lines of “all kinds of beasts.”
7-In Japanese culture, the type of rope Kaido wears as a belt, shimenawa, is used to denote that the area within it is important or sacred.
8-Kaido seems to be inspired by oni, ogre-like yōkai who are among the greatest icons of Japanese mythology.
Oni are usually depicted as having a giant, hulking frame, one or multiple horns on their heads, wild hair, and a fierce visage, traits shared by Kaido.
Like Kaido, oni are said to possess immense body strength. In addition, they are often depicted carrying kanabō as their signature weapon, like Kaido does.
Kaido’s residence on Onigashima (literally “island of oni/ogres”) is based on the tale of Japanese folktale hero Momotarō, who according to said tale, when matured into adolescence, went to defeat a band of oni dwelling on an island of said name.
A Japanese proverb is “oni no me ni mo namida” (鬼の目にも涙?), which literally means “a tear in the ogre’s eye”, saying that even the hardest of hearts can be moved to tears. This fits Kaido’s side as a maudlin drunk prone to weeping.
9-Kaido’s dragon form is that of a Chinese or generally East Asian dragon.
-Just as Kaido is said to be the world’s “Strongest Creature”, Eastern dragons are seen as symbolizing power and so are extremely powerful; either semi-divine or literal gods.
-Eastern dragons are associated with water as well as the weather (especially summoning rainfall). This may correlate to how Kaido appears to have limited ability to influence weather (or at least clouds).
-Kaido’s ability, as a dragon, to fly by generating clouds to use as footholds is based on Chinese dragons’ ability to magicially fly via clouds.
-Kaido’s dragon form is blue: in Chinese culture, the Azure Dragon (also “Blue Dragon”, “Green Dragon” or “Blue-Green Dragon”) is a Dragon God who (as one of the Four Symbols of the Chinese constellations) represents the East and spring season. In Japanese, the dragon is called “Seiryū”.
-Eastern dragons are commonly depicted with hair, including a wild mane, long, tendril-like whiskers appended to each side of their snout, and beard hair. This matches Kaido’s wild mane, long and thin mustache, and beard that he retains in his dragon form.
-Kaido’s dragon form has four claws/toes: four-clawed dragons are customarily depicted in Mongolia and Korea (as opposed to the three claws common for Japanese dragons). With respect to China, since its early days of imperial dynasty, four-toed dragons have been a symbol of imperial aristocracy (such as princes) and denoted imperial ranking below that of the Emperor himself (who was instead symbolized by five-toed dragons).
-Eastern dragons are depicted as chimerically amalgamated from multiple animal parts, and there is a saying of “9 resemblances”, which are commonly: the antlers of a deer, the head of a camel, the eyes of a demon, the ears of an ox, the neck of snake, the belly of a clam, the scales of a carp, the claws of an eagle, and paws of a tiger, but there are differing accounts. Further, in addition to assuming human form, Eastern dragons oft can transform into other animals too. All this may correspond to how Kaido is called “Kaido of the Beasts” and commands an army of pirates with animal-based powers.
-However, Eastern dragons do not typically breathe fire. Those who do were said to be sent from the heavens to earth as punishment. Kaido’s ability to breath a heat blast (contrary to Eastern dragon’s water association) could be more inspired by European conceptions of fire-breathing dragons or “firedrakes”.
10-Kaido’s habits to favor alcohol and to lose self controls are similar to the legend of Yamata no Orochi, a famous hydra like dragon and incarnation of floods, or a god of mountains and rivers in Japanese mythology.
His habits to favor alcohol and to lose self controls are also similar to Shuten-Dōji, lord of demons and bandits who was slain by famous Shitennō including Sakata no Kintoki (either son of an ogress and a Thunder God, or son of a red dragon and a woman in some legends), who is the inspiration source of Sentomaru. Both Yamata no Orochi and Shuten-Dōji were slain by being incapacitated with alcohol.