One interesting story could be about a new crew member joining the Big Mom Pirates. They might face challenges in adapting to the strict hierarchy and unique rules of the crew. For example, they have to deal with Big Mom's mood swings and the various powerful members already in the crew.
Big Mom herself is often a central and popular character. Her immense power and unpredictable nature make for interesting storylines. Writers can explore her relationships with her children and how she rules the crew.
One common trope is the underdog story. Your self - inserted character is often new and not very powerful at first compared to the established Big Mom Pirates. They then have to prove themselves. Another trope is the discovery of a hidden power or ability within the self - inserted character. It could be unlocked during a dangerous encounter with the pirates. And there's also the 'fish - out - of - water' trope, as the character is usually from a different background and has to adjust to the strange and often brutal world of the Big Mom Pirates.
To write an engaging Big Mom Pirates self - insert fanfic, first, really study the characters in the Big Mom Pirates. Know their personalities, goals, and relationships. For example, Big Mom herself is a complex character with a huge appetite and a strict family structure. Then, think about how your self - inserted character would fit into this world. Maybe your character has a special ability that can either help or challenge the pirates. Also, create interesting plotlines. It could be about a treasure hunt with the pirates or getting involved in their internal power struggles.