Another idea is that they time - travel in a loop. Every time they go back in time and change something, it creates a new future, but then they get sent back again because the change wasn't enough to break the loop. They keep meeting different versions of their friends and enemies in different time periods. It's a never - ending cycle until they figure out the key to break the loop and return to their normal time with a better understanding of how their actions can shape the future.
One possible plot could be that Luffy and Robin get sent back in time to the era when the Ancient Weapons were first created. They might have to figure out how to stop a powerful force from misusing the weapons. Luffy would use his determination and unique abilities, while Robin's knowledge of history and ability to read Poneglyphs would be crucial in understanding the situation and finding solutions.
One possible plot twist could be that Luffy and Robin travel back in time to the Void Century. This would open up a whole new world of exploration as they discover the true history of the world. They might encounter the Ancient Kingdom and learn the secrets that have been lost for so long. It could also put them in a dangerous position as they might be hunted by the World Government who wants to keep that history buried.
One possible plot could be that after many adventures and saving the world together, Luffy realizes his true feelings for Robin. They then decide to get married on their ship, with the whole crew celebrating.
In Robin and Luffy time travel fanfiction, a frequently seen theme is the exploration of history. Since they are time traveling, they get to see the One Piece world's past up close, which includes things like the origin of devil fruits or the history of certain kingdoms. Another theme is the strengthening of their bond. Through facing different challenges in different time periods together, their friendship and trust in each other grow even deeper. And of course, the theme of destiny also often appears. They might question if their time travel was fated and what role they are supposed to play in the different timelines.
Another idea is that they time travel to a random point in the past, like when Gol D. Roger was still alive. Luffy would be excited to meet the Pirate King. Roger might see something special in Luffy and give him some cryptic advice. Robin could ask Roger about the secrets he knew about the world's history. This encounter could have a huge impact on Luffy's journey and how he views his role as a pirate.
One common theme is self - discovery. When they travel through time, both Luffy and Robin often learn more about themselves and their capabilities. Another theme is the alteration of the timeline. They may accidentally or purposefully change things in the past, which then has consequences for the future. And of course, the theme of their relationship is always present, as time travel can bring them closer together in different ways.
One possible plot could be that Robin discovers an ancient text that leads to a powerful and mysterious treasure. Luffy, being eager for adventure, decides they must go after it immediately. Along the way, they face various enemies and challenges. Robin uses her knowledge to decipher clues, and Luffy uses his strength to fight off foes. They might also meet some old friends from the Straw Hat crew who join them on this new quest, making the journey full of reunions and new memories.
Robin, being more reserved and knowledge - seeking, would approach the time travel with a more cautious and inquisitive mindset. She would be interested in learning about the history and culture of the different eras. Her calm nature could balance out Luffy's impulsiveness. For instance, when Luffy wants to rush into a dangerous place, Robin might stop him and suggest they gather more information first.
For Luffy, time travel could make him more mature in a sense. He might start to understand the long - term consequences of his actions. For example, if he sees how his impulsive decisions in the past led to certain negative outcomes in the future, he could become more cautious. Robin would become even more determined in her pursuit of the truth. After seeing different historical periods, she would have more clues and might be able to piece together the full history faster.
Luffy's rubber ability might not change directly due to time travel, but his understanding of how to use it could be enhanced. For example, if he travels to a time where there are different fighting styles, he could incorporate new techniques. Robin's ability to sprout body parts on any surface could be used in really creative ways. If they travel to a time with different architecture, she could use the structures to her advantage in combat or for exploration in ways she hadn't thought of before.