Their relationship could start with Uta being initially distrustful of Luffy. After all, Luffy is a pirate and Uta has her own ideas about pirates. But as she sees Luffy's pure heart and his determination to protect his friends and pursue his dreams, she starts to warm up to him. They might then become friends who share their different stories and experiences.
They might have an epic battle to test Luffy's growth. Shanks could see how much stronger Luffy has become and be proud. Maybe Luffy will show off his new Haki abilities.
In fanfiction, when Sabo and Luffy meet again, they might have an emotional reunion. They could share stories of their adventures since they last saw each other. Sabo might show off his new skills or powers, and Luffy would be excited to see his brother again. They could also plan new adventures together, vowing to face any challenges as a team.
A different fanfiction could be set in a post - war scenario. Luffy has achieved his goal of making the world a freer place, and Uta, with her music, is now using her influence to bring joy and peace to the people. They team up to hold a grand concert on an island that was once ravaged by war, and their combined efforts help the island to revive and thrive.
Fanfiction.net is also a great place to find luffy and uta fanfiction. There are many talented writers who post their works there. However, the website's interface might be a bit old - fashioned compared to AO3. But it still has a good amount of content related to different anime and manga pairings, including luffy and uta.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - made stories, and you're likely to find some great 'uta x luffy fanfic' there.
Some 'uta x luffy fanfic' could explore a scenario where Uta joins the Straw Hat crew. This would bring a new dynamic as her musical powers and her connection to Luffy would add interesting plotlines. For example, she could use her music to enhance the crew's morale during tough battles.
There could be a luffy x uta fanfic where they meet in a different timeline. Uta's singing might have a special effect on Luffy, giving him new powers or a different perspective on his goals. This would lead to an interesting exploration of their relationship and how it affects the world around them.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics from various fandoms, including One Piece, so there's a good chance you'll find some luffy x uta fanfic there.