Sanji is the cook of the Straw Hat Pirates and one of their strongest fighters as well. Introduced in the story during Baratie, Sanji showed his worth to Luffy and ended up joining him on the journey to find the One Piece and become the Pirate King. He has his own dreams of finding the All Blue, a legendary ocean where fish from all over the world can be found.
Sanji is, first and foremost, a cook and he values this skill that he inherited from Zeff, his father figure, greatly. However, he is also an equally important fighter in the crew, being part of the Monster Trio, along with Zoro and Luffy, and, one of the Pirate King's Wings. While Sanji does not have a Devil Fruit, if you were to ever eat one, there are certain ones that would fit him perfectly.
5 Sui Sui no Mi
The Sui Sui no Mi, also known as the Swim Swim Fruit, is a Paramecia type of Devil Fruit that was eaten by Senõr Pink of the Donquixote Pirates. This Devil Fruit allows the user to treat their surroundings as water and swim in them freely. The user can even swim in the ground or the buildings around them.
Sanji is an excellent swimmer, having lived on an ocean-going restaurant for a significant portion of his life. In the entire crew, he is the second-best swimmer, after Jinbe, and his swimming abilities have previously been compared to those of Fishmen. This Devil Fruit would aid Sanji greatly and make him an excellent fighter on the ground. While Sanji says fighting aerially is his forte, this would make him a threat from both the skies and the seas below him.
4 Kuku Kuku no Mi
The Kuku Kuku no Mi is another Paramecia type of Devil Fruit that allows the user to create food out of nearly anything. This Devil Fruit power is currently wielded by Streusen of the Big Mom Pirates. It allows him to create different food substances out of nearly anything. For instance, he was able to turn a block of wood into meat with his powers. When the Whole Cake Château fell, following the explosion of the Tamatebako, he managed to turn the entire chateau into a cake.
Given that Sanji is a cook, this Devil Fruit would aid him greatly. The only problem with it is that the ingredients that it comes up with are not tasty, despite being nutritious. This could mean that Sanji would be against using its powers, however, with great cooking expertise, it is possible that this Devil Fruit can be made better under a proper cook.
3 Pika Pika no Mi
The Pika Pika no Mi is a Logia type of Devil Fruit eaten by Admiral Kizaru of the Navy. This Devil Fruit allows him to become light itself and manipulate it freely. Evidently, it makes him one of the fastest people in the One Piece world, as he becomes light itself. Kizaru is also able to hit with terrific weight, as great speed translates to great weight. Sanji is a fighter based on speed.
Fans have seen this from the very beginning of the story and he is likely the fastest Straw Hat right now. He has recently gained the ability to vanish with raw speed in Wano, which is staggering. With the Pika Pika no Mi, Sanji's Powers would grow even further and make him the fastest man alive. Furthermore, this would also make his kicks more dangerous than ever before. Sanji would be able to kick at the speed of light and that would mean his kicks become deadly. Furthermore, these kicks, when combined with the powers of Ifrit Jambe, would become even stronger and make him a monster in combat.
2 Goro Goro no Mi
The Goro Goro no Mi is another Logia type of Devil Fruit that allows its user to become lightning itself as well as manipulate and create it freely. This power is currently in the possession of Enel, who is on Fairy Vearth. The Goro Goro no Mi also makes the user incredibly fast, however, Sanji already has terrific speed that lightly surpasses that of lightning at this point in the story. This is evident from the fact that Niji can travel and hit at faster speeds than lightning and Sanji, after Wano, has far surpassed his brother.
The attack power that Sanji would gain with this Devil Fruit would be staggering. With the awakening of his latent scientific abilities, Sanji can now also generate electricity in his kicks with Ifrit Jambe. This electricity could be further improved with the Goro Goro no Mi. Furthermore, this Devil Fruit would also allow him to pick up all the radio waves from his surroundings and improve his Observation Haki. This Devil Fruit was primarily responsible for Enel's Mantra being exceptional and with Sanji, whose Color of Observation is already far superior to him, it would make him a monster.
1 Mera Mera no Mi
The Mera Mera no Mi is a Logia type of Devil Fruit, currently in the possession of Sabo, the Flame Emperor. It allows the user to become flames and create, as well as manipulate them freely. Sanji is a character that is greatly linked to fire. As revealed by Oda recently, Sanji has great resistance to fire, thanks to the genetic manipulation that he underwent. At the same time, all his attacks are powered up with fire. Diable Jambe sees him coat his legs and fire and attack with great ferocity.
Ifrit Jambe sees him take this to the very next level and generate blue flames, which burn much hotter than regular flames, on his feet, along with electricity as well. With the Mera Mera no Mi, Sanji would be able to generate more flames as well as gain a Logia body. Furthermore, he would also be able to attack with fire from a distance and that, when combined with the Black Leg Style, would make him a lethal fighter.