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.
To write a luffy x usopp fanfiction, you need to study their personalities thoroughly. Luffy is the fearless leader type, always ready for action, and Usopp is the inventor and storyteller. You could start by choosing a theme, say, 'overcoming fear'. Have Usopp face a really scary situation and Luffy be there to encourage him. Develop their dialogue in a way that reflects their unique voices. Luffy might say something like 'Don't worry, Usopp! We'll get through this!' Also, create a plot that has a clear beginning, middle, and end. Maybe they are trying to save a village on the island from a strange monster.
Sanji would go all out in cooking the most nutritious and delicious meals for Usopp to help him recover. He might also be a bit overprotective, not allowing anyone to disturb Usopp while he's eating. Chopper would be in full - on doctor mode. He'd be constantly checking Usopp's vital signs, giving him medicine, and trying to figure out the cause of the sickness. Robin would be quietly researching any possible cures or causes, using her knowledge of history and ancient texts.