For a long time, much of Sanji's history was shrouded in mystery, but Oda put an end to that during the Whole Cake Island arc. This allowed Sanji to take center stage and allowed the audience to learn far more about the character.
Sanji was easily one of the most memorable characters from the arc due to his complex relationship with his family. Seeing Sanji save his family, despite his hatred for them, was definitely one of the crowning moments of a very good arc.
10 Fighting Style
Sanji is notorious for his arsenal of kicks; he's an agile and flexible fighter who can launch a powerful kick from almost any angle. Sanji takes his job as chef very seriously and this led to him developing a fighting style that solely based on kicking. This is, of course, to protect his hands because Sanji would never forgive himself if he damaged the hands that he uses to carefully prepare meals. This fighting style has made a name for itself and Sanji was given the epithet of 'Black Leg' due to his potent kicking power.
9 All Blue
Sanji's main reason for joining up with the Straw Hats was to go in search of the fabled ocean known as the All Blue. The One Piece world is made up of four oceans. All these oceans contain strange and mysterious creatures. The All Blue is believed to be a part of the ocean where all these four seas meet. It is said to be a location where the rarest animals are said to exist. Sanji dreams of one day finding this ocean to use its marine life to enhance his skills as a chef.
8 Insane Levels of Lust
Sanji believes himself to be a gentleman, which admittedly is sometimes true. However, more times than not, he's just a flat out doting pervert. Sanji has a hard time controlling his excitement whenever he's around attractive females.
This lack of self-control often leads to him having massive nosebleeds which greatly hinder him from time to time. One such instance was during Fish-Man Island arc when he nearly lost his life due to a nosebleed he received after meeting a couple of mermaids.
7 Spirit of Fire
Sanji is a very passionate character who has an ever-burning spirit. This spirit often manifests in the forms of flames. Sanji can randomly ignite these flames whenever he chooses and they are capable of dealing serious burn damage. Sanji usually uses this heat-based ability in conjunction with his Daible Jambe techniques. When Sanji combines his kicks with the flames, his destructive capabilities greatly increase.
6 Post Time Skip
After training on Momoiro Island for two years, Sanji returned stronger than ever. Sanji spent a significant amount of his training running from the Okamas of the Kamabakka Islands, which increased his stamina, power and core strength. Being away from women for those two years also served to increase Sanji's passion and when he returns to Sabaody, he is capable of emitting more flames from his body and theses flames burn even hotter than before.
Sanji also went through a few design changes with the biggest being a change in hairstyle, which finally revealed the left side of his face that was always previously obscured.
5 Dedication To Crew
Sanji is a longstanding member of the Straw Hat Pirates, having joined during the East Blue Saga, after being invited onto the ship by Luffy. Since then, Sanji has committed himself to the role of the ship's chef. Sanji ensures to feed the crew with the best of foods with the highest nutritional value.
Furthermore, Sanji understands the value of feeding his crew well-prepared meals, as many pirates often die due to malnutrition and starvation. Like many of the Straw Hats, Sanji is loyal to the Straw Hats' ultimate mission and, on several occasions, he's sacrificed himself so that the dreams of his crewmates could continue.
4 Owner Zeff
After Sanji escaped from the evil and dastardly Germa Kingdom, he made his way around East Blue. Sanji then wanders around East Blue before he becomes a chef on a ship known as the Orbit. One day while at sea, the Orbit was attacked by Zeff. In an interesting turn of events, a thunderstorm comes out of nowhere and causes cataclysmic damage to both the Orbit and Zeff's ship.
Fortunately, both Sanji and Zeff survive but end up stranded on an island with little food. Later, it was revealed that Zeff gave Sanji what little food he had before eating his own leg for sustenance. This action greatly endeared Zeff to both Sanji and the audience at large, ensuring he goes down as one of the most loved One Piece characters.
3 Vinsmoke Lineage
Sanji was the third prince of the Germa Kingdom before being banished by his father, Vinsmoke Judge. Sanji's siblings are all genetically modified super-soldiers, but, due to Sanji's mother taking precautionary actions, he was born without the superhuman abilities of his siblings.
This led to much ridicule during his younger years, and his siblings would often gang up on him despite his clear physical inferiority. Sanji grew to deeply resent his family and one day, with the assistance of his sister, Reiju, Sanji finally managed to escape from the German Kingdom.
2 Vinsmoke Sora
Sora was the loving mother of Sanji. As one of the only Vinsmokes to ever show love and appreciation towards Sanji, the boy loved his mother with his whole heart. Sora always encouraged Sanji to express himself in whatever manner felt right to him and would encourage his cooking, even when his father would ridicule him for it. Sora had a kind and gentle heart and its clear that she's passed on much of those lovely traits to, at least, one of her sons.
1 Raid Suit
At the end of the Whole Cake Island Arc, Sanji received a Raid Suit from his brother, Niji. At first, he was reluctant to use it due to his chequered past with his family. Nevertheless, he eventually gets over this and uses the Raid Suit several times during the Wano Country arc.
With the Raid Suit on, Sanji becomes Germa's number 3, Stealth Black. This suit grants Sanji a number of power upgrades, inclusive of increased speed, power, endurance, and durability. Sanji's Raid Suit has the special ability to blend in with his background, granting him pseudo invisibility.