In the past, Usopp's abilities like his slingshot skills might be seen as more primitive compared to the advanced weaponry in his own time. But his creativity could give him an edge. For example, in a time when there were less advanced long - range weapons, his slingshot could be a very unique and effective tool. In the future, if he travels there, his abilities might seem obsolete at first. However, he could adapt by using his knowledge of old - fashioned combat and combine it with the new technology he finds.
First, know Usopp's character well. His traits like being a bit of a coward but also very brave when it counts, his love for inventing, and his loyalty to the crew. Then, come up with an interesting plot. It could be something like Usopp having to save the day with one of his inventions when the crew is in a tight spot. Also, make sure to keep his unique speaking style in mind when writing his dialogue.
To develop their relationship realistically, start with their existing friendship. Sanji often cooks for Usopp, so that could be a basis. Maybe Usopp starts to notice small things about Sanji, like how he cares for the crew through his food. And Sanji could see Usopp's growth in courage, which makes him respect Usopp more. From there, small moments of shared glances, and a bit of blushing when they accidentally touch could start to build the relationship.
Begin by deciding on the setting. It could be on the Thousand Sunny, during a battle, or on a new and strange island. For example, if you set it on the ship, you can start with Sanji cooking in the kitchen and Usopp coming in to ask for a snack. Their conversation can then lead to an adventure idea. Also, consider their goals. Maybe Sanji wants to create a new dish and Usopp wants to test his latest invention, and these two things somehow intertwine to start the fanfic story.
In some 'usopp fanfiction', he might be the key to solving a mystery on the ship. Maybe there are strange occurrences that only his unique perspective and skills can figure out. This could involve his talent for creating gadgets and his sharp observational skills, which are often overlooked by others but prove crucial in these fictional scenarios.
One common theme is empowerment. Since Usopp is often seen as a bit of an underdog, in female Usopp fanfiction, she is often empowered to be a strong and capable character. Another theme is friendship. Just like in the original story, the female Usopp forms strong bonds with her crewmates. Self - discovery is also a theme. She may discover her own abilities and what she truly wants in life through her adventures.