Charlotte Pudding could be a likely candidate. She has a complex personality. She's initially deceptive but later shows her true self. Luffy might be attracted to her vulnerability and the good side of her that emerges. And Pudding could be drawn to Luffy's honesty and his ability to see the best in people.
Yes, there are quite a few out there. You can check some popular fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'luffy marry boa hancock' and you'll find a variety of stories with different plotlines, from epic adventures where they face challenges together as a married couple to more slice - of - life type of stories that focus on their relationship in a more domestic setting.
Well, often you'll see the theme of love conquering all. Despite their differences, their love is what binds them. And also, the theme of growth. Both Luffy and Hancock might grow as characters through their relationship. For example, Hancock might become more open - minded about the outside world, and Luffy might learn more about the importance of relationships. Also, there's the theme of loyalty, as they are loyal to each other and have to prove it in different situations in the fanfictions.
Nami could also be a common character. She might help Luffy manage the financial aspects of his admiral duties, as well as use her navigation skills to assist in any navy - related voyages. And of course, she'd be there to keep Luffy in check when he gets too carried away.
Rayleigh would be a great candidate. He's an experienced pirate and has already trained Luffy for a while. He has a lot of knowledge about the world of pirates and could give Luffy a talk about the deeper secrets of the Grand Line or how to deal with the powerful enemies that lie ahead.
Happy might also become Luffy's friend. Luffy would be amused by Happy's flying ability and his cute appearance. Happy could also help Luffy navigate the Fairy Tail world, as he knows it well. And Luffy might share his food with Happy, which would make Happy very happy indeed.
He could face powerful sword - using pirates. Since Luffy now has a sword, he would attract the attention of other sword - masters in the pirate world. These opponents would test his new - found sword skills and force him to improve quickly.
Some fanfictions also pair Luffy with Hancock. Given Hancock's infatuation with Luffy in the original series, it's not a stretch to develop a full - blown love story. Her powerful status as a pirate empress and Luffy's carefree nature can create an interesting dynamic, with Hancock trying to win Luffy's heart while he is mostly oblivious to her romantic intentions.
She could be a former pirate captain herself. Maybe she was one of the most feared pirates in her time, and her skills and reputation were passed down to Luffy in some way, even if he didn't know it was from his mother.
As of now, in the manga, the identity of Luffy's mom remains unknown. There have been many theories and speculations among fans, but no official confirmation.