Another idea is to set the fanfiction in a different realm related to Fairy Tail. Maybe the new generation discovers a hidden dimension where the rules of magic are different. They have to adapt quickly and use their wits and powers to survive. It could also involve a new dark guild that is causing trouble in this realm, and the new generation has to stop them.
Base their powers on something unique. It could be related to their emotions, like a character whose magic gets stronger when they're angry. Or it could be tied to an object they carry, such as a necklace that gives them the ability to control water. Their powers should also have limitations, which can add to the drama and conflict in the story. For example, if a character can fly, but only for a short period of time before getting exhausted.
You could write about how the next generation faces a new, more powerful dark guild. They might have to learn from the past adventures of their parents while also coming up with their own strategies. This could involve training arcs where they master their magic in unique ways, different from their predecessors. And perhaps they'll find hidden powers within themselves that were dormant until this new threat emerged.
The children of Natsu and Lucy are often popular. Their combined powers and the legacy of their parents make them interesting characters. They might inherit Natsu's dragon - slayer magic and Lucy's celestial spirit magic, and their love stories could be full of action and magic.
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.
One possible plot is that the new generation accidentally travels to a time when Fairy Tail was just being formed. They get to experience the early days of the guild, the friendships being forged, and the challenges the original members faced. They might also have to deal with an old enemy that resurfaces due to their time - traveling interference.
Gray and Juvia's offspring could also be central characters. They could have an interesting mix of ice - make magic and water magic. Maybe they struggle with controlling their powers at first, just like their parents did, but in different ways. And their relationships with the other next - generation characters could be complex, adding depth to the story.
The children of the main Fairy Tail characters like Natsu and Lucy's kid, or Gray and Juvia's offspring could be main characters. They would inherit some of their parents' powers and personalities.
The children of the original Fairy Tail members could be main characters. For example, Natsu and Lucy's child might inherit their parents' magic and have a strong personality. They could lead the new generation in various adventures.
One idea could be that the new generation has to face a powerful dark guild that is threatening the academy. They might discover new magic types along the way. For example, a character could find a lost ancient magic within the academy's hidden chambers.