There were a few novels that were similar to Luffy's brother that he could recommend. Among them, One Piece: The Fruit of Rotation and One Piece World's Cultivation Journey are two novels recommended to you. The main character of One Piece: The Twirling Fruit was Luffy's subordinate. In the later stages, he was a BOSS, but he was not invincible. The main character in One Piece World was Luffy's brother. He became stronger step by step in One Piece and protected his brother. These two novels might meet your requirements for Brother Luffy.
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.
There could be an original character created just for the fanfiction. A woman with a kind heart but a tough exterior, who was a great fighter. She could have met Luffy's father during a battle and they fell in love, and she became Luffy's mother.
Naruto might give Luffy training in stealth. Since Naruto is a ninja, he is well - versed in moving around unnoticed. Luffy, on the other hand, is more of a straightforward fighter. So Naruto could show him how to approach enemies without being detected first, which would be a new and useful skill for Luffy in his pirate adventures.
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.
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.
Common themes in 'naruto luffy brother fanfiction' include power - sharing. Given their unique abilities, fans like to write about how they would teach each other or combine their powers. Also, friendship is a big theme. Even though they are brothers in these stories, their relationships with other characters from their respective worlds are still important, and the fanfictions often explore how they maintain those friendships while being brothers. And of course, there's the theme of family. The idea of them being brothers brings in a whole new family dynamic that wasn't present in the original stories.
Well, there is some 'naruto luffy brother fanfiction'. Some of them explore how their different powers would interact if they were brothers. For example, Naruto's ninjutsu and Luffy's Devil Fruit abilities could make for some really exciting adventures together. Also, the different worlds they come from, the Hidden Leaf Village and the Grand Line, could be combined in creative ways in these fanfictions.
They could go on an adventure to find a powerful treasure that combines the power of the One Piece and some kind of ninja - related artifact. Maybe they'd have to fight against a new enemy that is a combination of pirates and rogue ninjas. They might travel to new islands where Naruto's ninjutsu would be useful for exploring hidden caves, and Luffy's stretching ability would help them reach high places or cross large gaps.
Rebecca could potentially be in Luffy's harem. After Luffy helped her in Dressrosa, she might develop feelings for him. She is a strong - willed and kind - hearted character. Another could be Shirahoshi. Luffy has a special connection with her as he saved her from being captured. Her gentle and innocent nature would contrast with some of the other more assertive members of the harem.