@Reborn when Hancock hit Smoker in MF, the latter said « Ugh the Kuja haki! » as if they have a specific haki technic.
When Luffy was on Amazon Lilly we saw that the Amazon was using :
-Invisible haki on arrow to make them stronger
-Deflection haki
In Wano they are using :
-Koka on blade
-The action to cut or not cut something
-Black blade
Hyo who was call the « mighty sword » did not know how to use « penetration » even tho he knows what it is.
So my guess is that the Kuja choose the invisible haki branch while the Wano samurais took the koka’s one. This for me further proves the two branchs. I see this like this :
-Level 1-
Invisible haki on limbs (Luffy vs Pacifista)
Koka on limbs (Luffy vs Kraken)
Technics: Fullbody koka or flaming koka
-Level 2-
Invisible haki on weapon (Tashigi vs Monet)
Koka on weapon (Zoro vs Pica)
Technic: Flaming koka
-Level 3-
Invisible haki on solid object with no contact with the body (Margaret’s arrow)
Koka on solid object with no contact with the body (Katakuri’s Chikara mochi)
Technic: invisible haki or koka on non-consistent object
-Level 4-
Invisible haki « Deflection » (Raileigh vs Elephant)
The ability to cut or not what you want ( Zoro vs Mr1)
-Technic: using level 1 koka and deflection at the same time
-Level 5-
Invisible haki « Penetration » (Raileigh vs iron collar
Black blade
-Technic: use penetration and level 1 koka at the same time
Specificity of invisible haki : Lighter, less tiresome, can be mix with element without making them solid, can deflect any thing, can destroy thing from inside
Specificity of koka : Heavier, more tiresome, can be mix with devil fruit, enhance the hardness of any weapon, allow the user to change the form of something, can definitely change the nature of something
Furthermore Koka has strength level:
Level 1: Black and white (Luffy most of the time)
Level 2: Black and red ( Luffy in « Snakeman »)
Level 3: Black and blue (Katakuri’s koka)