Perhaps she was originally from a planet that the Rebels are trying to protect. When she discovers this, she has an internal struggle. She could befriend a rebel who makes her see the Empire's true nature. This friendship could be the turning point for her character. She might then use her stormtrooper training and equipment to assist the Rebels in their fight against the Empire.
She might be a redeemed character. Start off as a loyal stormtrooper but then, after experiencing some events like seeing the Empire's cruelty towards innocent civilians, she defects to the Rebels. In the fanfiction, she could bring with her knowledge of Imperial strategies and weaponry that prove invaluable to the Rebels.
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.
One possible fanfiction could be about Numa's growth within the Rebellion. Maybe she discovers a new ability that helps the Rebels in a crucial battle. For example, she could have an uncanny sense for detecting Imperial traps, which she uses to lead the Rebels to safety and victory.
One great 'Star Wars female stormtrooper fanfiction' is 'The Female Stormtrooper's Journey'. It tells the story of a female stormtrooper who discovers a hidden truth about the Empire and decides to defect. Another is 'A Female Stormtrooper's Redemption' which focuses on her efforts to make amends for her past actions in the service of the Empire.
One common theme is redemption. Many stories focus on stormtroopers breaking away from the Empire's control and finding a new, more moral path. Another is identity, as they often question who they are within the strict hierarchy of the Empire.
Once upon a time, I found myself inside the body of a Stormtrooper. I was on a mission on the sandy planet of Tatooine. The blaster in my hand felt heavy. I followed my squad blindly at first, but then I started to question our orders. Why were we hunting rebels who seemed to be fighting for a just cause? I decided to secretly help a group of rebels escape. It was a risky move as I could be court - martialled if caught. But I couldn't just stand by and be a part of the evil Empire's deeds.
There could be a fanfiction where Ezra, from Star Wars Rebels, discovers the legacy of Revan. Maybe Ezra stumbles upon an ancient Jedi artifact that has a connection to Revan. He starts to have visions of Revan's battles and is inspired by his unique blend of light and dark side use, which could lead Ezra to question his own understanding of the Force.
In many Star Wars Rebels fanfictions, Ezra's crying moments can be quite impactful. It might be due to the loss of a mentor or a difficult situation. For example, if Kanan died in the fanfiction, Ezra would be devastated and his crying would show his deep emotional bond with his master.
A fanfiction centered around Dawn Syndulla could explore her relationships. She might develop a close friendship with a new character, perhaps an alien from a species she has never interacted with before. Their adventures together, learning about each other's cultures and helping the Rebellion in the process, could be a great plot for a story.
A fanfiction could explore what would happen if Anakin Skywalker had survived and joined the Rebellion during the events of Star Wars Rebels. He would bring his incredible combat skills and Jedi powers. His relationship with other characters like Hera Syndulla and Sabine Wren would be interesting to develop, as they would have to learn to trust this once - fallen hero.