Obviously, Jellal and Erza are the main characters as they form the core of the Jerza family. Their relationship is central to the fanfiction.
One of the main themes is redemption. Jellal has a lot to atone for, and his relationship with Erza is often intertwined with his journey towards redemption. For example, in many fanfics, Erza's belief in Jellal gives him the strength to keep trying to make up for his past mistakes.
One idea could be exploring how Jellal and Erza start their family. Maybe they adopt a child with a special magic ability and the story could revolve around how they teach the child to control their power while also facing threats from old enemies who want to use the child's power for evil.
Natsu could be a main character. He could be the hot - headed but kind - hearted student who always gets into trouble but also manages to save the day with his powerful fire magic. His loyalty to his friends would be a key aspect in the fanfiction.
Well, Naruto is a given as the main character who is being raised in the Fairy Tail environment. Gray would be an interesting addition. His cool - headedness could contrast with Naruto's sometimes impulsive nature. Erza would also be a key character. She could be like an older sister figure to Naruto, teaching him discipline and how to handle difficult situations, both in battles and in the guild.
Natsu could be an unexpected main character. He might accidentally end up in the bra section while looking for something else and then get roped into helping the girls pick out bras. His naivete and comical reactions would add humor to the story. And of course, Levy. She's intelligent and could use her knowledge to find the best deals and the most unique bras in the store.
Natsu Dragneel could be a main character. He's known for his fiery spirit and powerful fire magic. At the academy, he could be the troublemaker who often gets into scrapes but also has a heart of gold and is always there to help his friends. His dragon - slayer magic would make him stand out among the students.
The children of Natsu and Lucy would be great main characters. Their combined magic powers, with Natsu's fire and Lucy's celestial spirit magic, could create a really interesting character. They might inherit a special ability that comes from the combination of their parents' magic.
It's hard to say without actually reading it, but it could feature the classic Fairy Tail characters like Natsu, Lucy, Gray, and Erza. They are the most popular and central to the original series.
Lily could be a main character. He's Gajeel's loyal Exceed companion and has his own set of skills and a unique personality. Another could be Gajeel's family members like his parents if they are introduced in the fanfiction. They would bring in new perspectives and storylines related to Gajeel's past and family history.
One great fanfiction is 'A New Adventure'. It beautifully develops the Nalu relationship. It has exciting plot twists that involve the whole Fairy Tail guild. The Gruvia moments are also really sweet, showing how their relationship has grown over time. Jerza's interactions are written with great detail, staying true to their characters. And Gale's dynamic adds an interesting layer to the story.