This is merely speculation as we don’t know much about Kaido, However, I am seeing a trend in the Yonko.
As Big mom seems to display signs of dissociative identity disorder, Kaido seems to be a deeply depressed character.
In Kaido we are given a character that has reached almost the pinnacle of his territory. And yet, something more seems to be at work. When we see Kaido he is either extremely angry or very depressed.
He has also tried to kill himself multiple times. However, this does not seem to be a hobby, more like a cry of pain.
From what we know of Kaido he is a beast wanting to die, as such, we must wonder what has transpired in his life for this to happen.
Yes, he has been captured and tortured, but he does not seem to recover from these losses well. He seems to carry the burden of this loss almost like a chain around his neck.
In fact, he has become so disdained by life that all he wants is death, to the point of looking for new ways to die.
Yet, what if Kaido is the representation of suicide in One Piece? What if Kaido like Big Mom has a bigger role to play in Oda’s Story. That role is to represent the mental health aspect of characters that we don’t pay attention to.
He may be a symbol of what so few people pay attention to and don’t understand, that being suicide. In this sense, Big Mom and Kaido seem to represent two coinciding pains of life mental illness and suicide.
They may represent the over exaggerating people see in their minds. They could, however, be Oda’s tools to make people pay attention to life struggles few see.
This is merely speculation but is quite possible.
*Theory by Rhodehawk