True Black Leg is a fighting style that utilizes only the legs as the arms are reserved for cooking.
It is used by Sanji can be obtained by training from Sanji (Located iN Second Sea at Wano) for B$1,000,000,000, 2.8k strength, 2.5k haki, and 2k defense.
Some people when they talk to him it says "alright let your quest begin talk to me again to learn your objective" when you talk to him again he says the same thing, you will need double jamble before starting the quest, (you can get it back in first sea, talk to sanji again and he will make you pay for a upgrade to black leg, Makes your diable jamble be in both legs)
sanji npc
True Black Leg can also be evolved into Ifrit black leg, You will need Exoskeleton, Germa Race
This fighting style is used by Sanji.