Love and redemption are very common. Jellal has a lot to make up for, and Erza often represents his path to redemption, so their love story is intertwined with his journey of becoming a better person.
One common theme is their shared history. Given their past interactions in the original story, many fanfics explore how they come to terms with what happened between them before. Another theme is friendship. Even if they have a complex relationship, the idea of them being friends and having each other's backs is popular.
I don't encourage or promote 'lemon' fanfiction due to its often inappropriate nature. But generally, if we were to consider just the relationship aspect in non - inappropriate fanfictions of Jellal and Erza, they often show a complex relationship. Jellal has a troubled past which makes their relationship full of emotional turmoil and the potential for great character growth and development in the story.
Love and redemption are common themes. Given their past, Jellal has a lot to atone for, and in many fanfics, Erza's love becomes a part of his redemption journey. Another theme is the struggle between duty and personal feelings. They both have important roles in their world, and finding a balance between that and their relationship is often explored.
Some fanfictions might focus on the reactions of their friends and comrades in their respective guilds. Their friends could be excited, offer support, or in some cases, be a bit worried about how having a baby will change the dynamic of the group. It adds an interesting layer to the story as it shows the impact on the larger community around them.
In a Jellal and Erza married fanfiction, their life could be filled with adventure and understanding. They might travel together, using their combined skills to protect the weak. Jellal's past mistakes would be something they've worked through, and now they support each other fully. Erza would bring her strong will and sense of justice to the relationship, while Jellal would offer his intelligence and new - found sense of redemption.
Yes, there might be some. Some fanfiction writers focus on the relationship between Erza and Jellal in a more innocent and family - oriented way. They could write about their journey towards starting a family in a very sweet and non - explicit manner. For example, they might write about how they handle the news of pregnancy with love, support and anticipation for the future. It could involve scenes like them preparing a nursery or sharing the news with their friends in Fairy Tail in a heartwarming way.