Typically, megumi fanfic often focuses on his personality traits. His stoicism and determination are often highlighted. For example, in many fanfics, his unwavering resolve in the face of danger is a central theme.
Well, Megumi's story in the manga was full of twists and turns. She had to overcome various obstacles, and there were also some unexpected developments in her relationships with other characters.
As of the latest chapters I've read, Megumi is still alive in the manga. Usually, such major character deaths are significant plot points and would be well-publicized if they occurred.
One possible theme could be friendship. They might start as acquaintances and gradually become close friends, sharing secrets and having each other's backs. Another theme could be about loyalty. For example, in a dangerous situation, they remain loyal to their group and to each other.
Often, they highlight their shared love for food. Since they are both in the culinary world in the original story, fanfics usually revolve around cooking challenges they face together or how they teach each other new techniques.
One common theme is his growth as a sorcerer. Many fanfics focus on how he hones his skills and becomes stronger. Another theme is his relationships, like his friendship with Yuji or his complex connection with the Zenin family.