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.
There have been many parallels between Wano and the story of “Momotaro no Monogatari” confirming Kaido being Oni.
This origins with Momonosuke’s reveal, the reveal of Kaido’s design and the foreshadow of Onigashima.
Onigashima is inspired by the island with the same name, appearing the story of “Momotaro no Monogatari”.
Yes and on this island the evil Oni king is housing to be fought by the protagonist(s) and his animal retainers. This Oni within the One Piece story is portrayed by Kaido and hence the big community question exists, wether Kaido is an Oni.
Hitetsu said that the sword Enma is able to “cut through to hell itself” while the Ame no Habakiri is able to “cut even the heavens”. So Enma is able to “cut through hell”. Now where does the devil live? In hell.
Enma wis the only weapon known to have harmed Kaido.
Just thought this might be worth sharing since it adds up to the Kaido oni theory.
*Theory by zoxh1337