To develop a Stormtrooper character, you can focus on their backstory. Maybe they were conscripted against their will. This would give them a reason to be conflicted about their loyalty to the First Order. For instance, they might remember their family they were taken from and secretly long to return to them.
Once upon a time, there was a little kid who dreamed of being a stormtrooper. One day, he found an old stormtrooper helmet in a junk yard. He put it on and immediately felt like a real hero. He started to imagine himself on exciting adventures, fighting bad guys and protecting the galaxy.
Once there was a stormtrooper named TK - 421. He was always alone. His comrades didn't really care about him. He was just a number in the vast army. One day, during a battle, he got separated from his unit. He wandered in the desolate battlefield, hearing the blasts all around. He knew he was likely to die alone, forgotten by the Empire he served so loyally. It was a truly sad fate for a stormtrooper.
One popular type might be those that focus on a female stormtrooper's journey within the First Order. For example, a fanfic could detail her experiences during battles and how she overcomes challenges. Another could be about a female stormtrooper who discovers a hidden side of the First Order and decides to rebel.
Kids can learn about courage. Just like stormtroopers face dangerous situations, kids can be brave in their own lives, like standing up to a bully at school.
You need to do some research on the Star Wars universe, especially about stormtroopers. Know their training, equipment, and how they operate within the First Order. This knowledge will make your fanfic more believable. Also, think about the setting and how it will affect your character's actions.
Probably the lack of identity. They are just numbers in the Empire's military. No one really cares about who they are as individuals. For example, if a stormtrooper dies, they are quickly replaced, and no one mourns their loss.
Another concept could be a crossover of the two universes' technologies and magic. Maybe the Stormtroopers are trying to harness the power of magic for their own purposes, like creating more powerful weapons or defenses. And the wizards are both intrigued and worried about this new development.
One common theme is identity. Female stormtroopers often struggle with their identity within the Empire. Another theme is redemption. They might try to atone for their actions as part of the Empire. And also, friendship can be a theme, like making friends with other characters, either from the Empire side or the Rebel side.
Well, perhaps the female stormtrooper witnesses Darth Vader performing some act of incredible power. She becomes intrigued and starts to follow him secretly. Eventually, Vader notices her and tests her loyalty. She passes his tests and he then assigns her special missions that no other stormtrooper could handle, like infiltrating a rebel base that has some sort of dark side artifact he desires.