The two universal forms are Armament Haki and Observation Haki, also known as Busoshoku no Haki and Kenbunshoku ... of Logia-type users’ bodies in One Piece and can be applied to one's own ...

After going through all of the God's Knights appearances, I've figured out why none of them have used Haki so far, and One ...

This is where Haki comes in; Haki is the physical manifestation of a person's spiritual energy (will). Among all the attacks in One Piece, Haki is the most effective way of hurting a Devil Fruit user.

Ever since the very first chapter of One Piece, Devil Fruits and Haki were introduced as the primary power systems of the world, despite the latter only being fleshed out properly later on.