Black Leg Style/Diable Jambe

A lot of people call it his signature technique but I can only remember him using it a few times, first to finish off kuroobi, then using the diable jambe version against a pacifista, a beast pirate, and against queen with zoro

There are characters who create and Control Fire in many fantastic productions, such characters in One Piece. But don't you think there are no characters in the One Piece universe who do a little too much fire attacks? We've been seeing characters setting themselves on fire or throwing flaming things since the East Blue Saga. But there are characters who use fire completely, except for the characters who only use fire in some of their attacks, the first of them was Ace. Ace is perhaps the character who uses fire most extensively, thanks to Mera Mera no Mi, the devil fruit he ate. Afterwards, we saw characters who use fire abilities just as well, although not as comprehensively as Ace e.g. Sanji, Marco, Akainu, Oven. We have now learned that a nut race has the ability to create and manipulate fire. What do you think about this subject? Are you satisfied that there are so many fire users? Do you think that the character who can create so much fire with devil fruits or techniques reduces the value of Mera Mera no Mi? I mean, don't you think the fact that there are so many fire users in the series makes Mera Mera no Mi ordinary? Would you like to see more devil fruits that can create Fire in the series?

Everybody knows Sanji, martial arts black leg and his move Diable Jambe. In the pre time skip era whilst fighting against Jabra and Oars he spins really fast to burn his feet. But post time skip, (perfect example is him fighting against Luffy.) he just puts his legs up and it just burns. I don't have the mangas after the timeskip so I dont know if they explain it in the manga. And if they tell it in the anime, i dont remember it(probably wasnt paying much attention.) How does he do this? I dunno and if you know pls tell me.