Ifrit Jambe is a Fighting Style in the First Sea (Upgraded version of True Black Leg.) where you can get it from[1] the Ifrit Sanji NPC on the Germa 66 island. To get it you need the Germa Race, Exoskeleton (Which can be bought at First Sea on Germa 66 for $50 Billion by the Germa Doctor, and you need the Germa Race in order to buy it.), and True Black Leg. Ifrit Jambe is an upgrade for True Black Leg.
PS: You don't need to grind anymore stats to get Ifrit Jambe, all you need is True Black Leg, Germa Race, and Exoskeleton.
I hope this page helped you. big thanks to monkeman732 for creating this page I fixed the grammar. :\