One common theme is growth. You see James Potter grow from a bit of a troublemaker to a more responsible person because of his love for Lily. Lily also grows in her understanding of James. Additionally, the theme of family is important. Their future family, especially with Harry, is sometimes hinted at in the fanfictions. The war against the dark forces is also a theme that often comes up, as it affects their relationship and their lives.
One common theme is their relationship development. It often starts from their initial dislike or indifference to each other, like in the books, and then gradually grows into love. For example, in many fanfictions, James has to work hard to change Lily's perception of him from a bully to a worthy partner.
The theme of growth is often present. Both James and Lily grow as individuals and as a couple in many fanfictions. They learn from their experiences, become more empathetic, and this growth is what cements their relationship in these stories.
In many fanfictions about them, the theme of sacrifice is present. Given the dangerous wizarding world they live in, they might have to sacrifice personal desires or safety for each other. Also, the theme of family is important. Since they end up having a family together, stories often explore how their relationship sets the foundation for the Potter family, and how their love influences their future children, like Harry.
I really like 'James and Lily: A Love Story'. It delves deep into their relationship, starting from their initial dislike for each other to their deep, abiding love. It also includes some really interesting side plots involving their friends like Sirius and Remus. And 'Potter's Love' is also a great read. It shows how their love survived the challenges of the wizarding world around them.
A great fanfiction could be about their courtship. James could write her love letters filled with his thoughts and feelings. Lily would keep these letters hidden away, reading them when she was alone and slowly falling more in love with him through his written words.
One possible fanfiction could be about how James Potter first fell in love with Lily Evans. Maybe it started in the Hogwarts corridors. He saw her kindness as she helped a first - year student find their way. This simple act made James look at her in a new light. From then on, he tried to be less of a show - off around her.
One great 'Lily Evans Potter Fanfic' is 'Lily's Journey'. It delves deep into her character, showing her growth from a young witch at Hogwarts to her role as Harry's mother. Another is 'The Lily We Never Knew' which focuses on her relationships with her friends and how she influenced the wizarding world even before Harry was born. And 'Lily's Legacy' is also good as it explores the impact she had on the fight against Voldemort through her sacrifice.
Petunia could be an important character. She might be grudgingly attending the wedding, still having mixed feelings about Lily's magical world. Her presence could add some tension as she struggles to fit in. And then there's Dumbledore. He could make an appearance and give some wise words of advice to the couple, perhaps about the future challenges they might face together.
The popularity of Lily Evans and James Potter fanfiction lies in the fact that their relationship is full of potential for exploration. We know they are Harry's parents, but there are so many gaps in their story. Fanfiction allows fans to fill those gaps, like how they really fell in love or what their lives were like at Hogwarts before Harry was born.