A great fanfiction idea could be that Lucy and Leo get transported to an alternate dimension. In this dimension, the rules of magic are different, and they have to figure out how to get back home while also dealing with the strange new magical creatures and challenges there. This would test their relationship and their individual skills.
There might be a fanfiction where Leo and Ar are faced with a great danger that threatens the Fairy Tail guild. They have to use their unique skills and the power of friendship to save everyone. For example, they could be up against a dark wizard who has a plan to destroy the guild, and Leo and Ar are the last hope. They start by gathering information, then formulating a plan that involves their combined magic abilities and the help of some of their guildmates.
In some fanfictions, Hughes and Lucy could be in a love triangle with another character from Fairy Tail. This would create a lot of drama and tension. For example, if there's a misunderstanding between Hughes and the third character about Lucy's feelings. It could lead to some intense confrontations and emotional moments as they all struggle to figure out their relationships within the context of the Fairy Tail guild.
A popular fanfiction idea is that Lucy and Sting are transported to an alternate dimension. In this strange new world, they have to rely solely on each other to survive. They learn to work together in ways they never thought possible. As they search for a way back home, their relationship blossoms into a strong partnership filled with mutual respect and admiration.
A plotline could also involve Lucy having to team up with an unlikely group of characters, perhaps some former enemies or characters from other guilds. Together, they have to face a common threat that is much larger than any of them could handle alone. This forces Lucy to use her wits and her magic in new and creative ways, and also develops her relationships with these new allies in unexpected ways.
A fanfiction could also explore a scenario where Lucy and Juvia enter a magic tournament together as a team. They face various opponents and use their combined skills to win. Their opponents might underestimate them at first because they seem like an unlikely pair. But they prove everyone wrong with their strategic use of magic. Lucy could summon spirits to distract opponents while Juvia attacks with powerful water spells.
There could be a fanfiction where Virgo and Lucy accidentally switch powers. Lucy has to figure out how to use Virgo's powers of earth manipulation and tunneling, while Virgo has to deal with summoning celestial spirits. This situation creates a lot of humorous and also some tense moments as they both struggle to adapt and still complete their tasks in the Fairy Tail guild.
In some fanfictions, their relationship develops through shared battles. As they fight side by side against enemies, they start to trust each other more and more, which deepens their connection.
One idea could be a crossover where Naruto and Lucy team up to fight a common enemy. Maybe a powerful dark mage from Fairy Tail's world has somehow made its way into the Naruto universe and is causing chaos. Naruto's ninja skills combined with Lucy's celestial spirit magic would make for an exciting battle.
One interesting concept could be exploring how Lucy from Edolas adapts to the Fairy Tail world. Maybe she has different magical abilities or a unique perspective on friendship compared to the original Lucy.
One idea could be a story where Jackal and Lucy are forced to team up during a mission. Maybe they start off not getting along but gradually learn to respect each other's skills. For example, Jackal's combat abilities combined with Lucy's celestial spirit magic could make for some really cool battle scenes against a powerful enemy.