@Kaido D. Stronger
https://en.wikipedia.org/wiki/Ryūjin
Kaido is revered and honoured as the protector of Wano as we saw in chapter 921. Ryujin is worshipped in the Shinto religion as a kami. The Shinto religion is the biggest religion in Japan as of today seeing that it's practised by 54% of its population. Now, it's not a religion per se since it has no offical creed or theology so it has more to do with rites and rituals that's connected to animism, the belief that all of nature is animated and possesses a life force and a soul (which in essence is what a kami is and what Shintoism is about).
Seeing that Ryujin is a kami of the ocean, agriculture and fishermen, this kind of fits the profile of Wano as of right now seeing that a lot of the food and water is contaminated, and so by worshipping him they pay homage to their kami for more auspicious times in whole of Wano. The sea is also treacherous and dangerous, hence, worshipping Kaido who is seen as a sea deity makes a lot of sense.
In Japanese mythology the Ryujin is the sea God that controls all sea living creatures. He lived in the magical underwater palace called
Ryūgū-jō palace and is also the father of Toyotama-hime (Otohime?) whose grandson, Jimmu, is said to be the first emperor of Japan. Ryujin is therefore viewed as one of the ancestors of the Japanese imperial dynasty (perhaps there exists some similar folklore around Kaido who is seen as the saviour of Wano).
Dude, Kaido is a Ryujin, and it directly ties to Fishman Island