1-As one of the Yonko, Kaido is among the 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-The episode of his physical anime debut aired on the 1st of May, Kaido’s birthday. In the anime, the color palette of Kaido’s dragon scale tattoo is very similar to the coloration of Doflamingo and Caesar clown’s SMILE.
3-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.
4-Kaido’s name may be based on the Japanese liquor, kaidou (海童).
5-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.”
6-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.
7-Kaido seems to be heavilly inspired by Oni of Japanese mythology. Common traits include horns, a massive stature, and use of a kanabō club as a primary weapon.
8-Kaido appears to have eaten a Mythical Zoan-type Devil Fruit that allows him to turn into a serpentine dragon.
His dragon form has very long beards and 4 toes on each arms. These characteristics correspond to that of Korean dragons than other east-asian dragons.
Dragons with flamboyant, colorful, warm colored bodies, and transform into humanoid forms including dragon kings, are much more common on Eurasian continent including India than in Japan.
9-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.
10-In the 6th Japanese Fan Poll, Kaido ranked as the 96th most popular character in the series.