User blog comment:Uraharattack/King and his Haki/@comment-180.190.91.165-20190123023421/@comment-2600:1702:3C50:A6E0:10D6:1168:EE77:CA21-20190123053708

We will see if these theories have any validation, but until then it is fun to explore possibilities. If I may say something in regards to Sanji's abilities, I think that his ability to set his leg on fire is sperate from his haki. I see it as a modification of the fire skates technique that Wanze used on the sea train to try and fight Sanji. Obviously it is a similar technique creating heat from friction, but since Sanji couldn't very well create friction in the same way since he is not wearing skates he had to spin to ignite his feet. Just my opinion.