I think it might have been a character introduced to add depth to Sanji's backstory and motivations. But without more context, it's hard to say for sure.
The key elements in Sanji's back story are his family, the Vinsmokes. His different nature compared to his siblings is also important. And of course, his love for cooking.
Sanji's back story is quite interesting. He grew up in the Vinsmoke family, which was a rather cruel and power - hungry family. Sanji was different from his siblings, he had a kind heart. His father was disappointed in him for his soft - heartedness and lack of the 'killer instinct'. Sanji was constantly bullied by his brothers. But he found solace in cooking. This led to his great passion for cooking later in life.
Fanfiction often explores Sanji's growth by putting him in challenging situations. Maybe he has to cook in a completely new environment or with limited ingredients. This forces him to adapt and innovate, which in turn shows his determination and resourcefulness. His character also develops as he learns from his mistakes in these situations and becomes an even better chef.
Another characteristic is the exploration of new relationships. Since Sanji is a popular character, in female - centered fanfiction, new relationships with female characters can be created. These relationships can range from romantic to platonic, and they add new dimensions to Sanji's character. For instance, he might form a strong friendship with a female swordsman in a fanfic.
Yes. The conflicts between Sanji and Luffy in the manga often stem from complex circumstances and character developments that drive the narrative forward.
One great fanfiction could be about their adventures on a new island not shown in the original story. Maybe they encounter a powerful and strange new enemy. Luffy's determination, Zoro's strength, and Sanji's culinary skills all come into play in this new situation.