One popular theme is adventure. Since both Jellal and Lucy are from the Fairy Tail world which is full of adventures, many fanfictions incorporate them going on quests together. They might face powerful enemies and rely on each other's strengths to overcome difficulties.
One popular theme is adventure. They might go on a quest together, facing various challenges. Another is the theme of friendship turning into love, as they get to know each other better through different situations.
One common theme could be the reaction of their friends and the surrounding community to the pregnancy. Another might be how Jellal and Lucy themselves adjust to the new situation.
The theme of self - discovery is common too. Through their relationship and the kiss, both Lucy and Jellal might discover new sides of themselves. Additionally, there could be a theme of protection, where the kiss is a way of showing that they will protect each other in the face of danger.
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.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions on various topics, including 'lucy x jellal' ones. Just use the search function there.
Some fanfictions might explore the idea of Jellal and Erza learning about parenting. They could be attending classes or getting advice from older, more experienced characters. There might also be a plotline where the pregnancy has some sort of magical complication that they have to figure out how to deal with, using their unique skills and the power of their love for each other.
Another common plot is a sort of redemption arc for Jellal within the fanfiction. In the Medevel world, he tries to make amends for his past wrongs towards Erza. This could involve him protecting her from various threats and in the process, their relationship deepens and evolves into something more romantic. Maybe he saves her from a dragon or an evil sorcerer.
One common theme is adventure. Since they are both from the Fairy Tail world which is full of adventures, fanfictions often put them together in new and exciting quests. Another theme could be friendship development. They might start as acquaintances and gradually become closer friends or even more.
You can try fanfiction websites like FanFiction.net or Archive of Our Own. They have a large collection of fanfictions. Just search for 'Jellal x Lucy' on the search bar and you'll get a bunch of results.
One popular plotline is the redemption arc of Jellal. Fans often write about how he tries to make up for his past wrongs towards Erza. For example, he might protect her from new threats in the Fairy Tail world. Another plotline is their relationship development. Writers may show how they gradually overcome their past traumas and start to trust and love each other again. Sometimes, they are put in a situation where they have to team up against a powerful enemy, which further deepens their bond.