User blog comment:Kaido King of the Beasts/Chapter 908: Imminent, Imbalanced, Improbable Whims/@comment-53539-20180618202404/@comment-3986064-20180619233532

I had a small realization but... Shirahoshi is Poseidon, one of the 3 ancient weapons and there is the mention of a secret treasure in the Holy Land - which we can speculate is that giant straw hat. I find absolutely no other similarities about these individuals other than the fact that they are irregulars:

One is Poseidon

Another has a straw hat

Another has two devil fruits

And another is of equivalent descendence as the Celestial Dragons, but her ancesters denounced that status.

The other thing that I can find about them having in common is that they seem to be more recent threats while Kaido, Shanks and Dragon are older threats, which are well understood.