If Lucy and Juvia leave Fairy Tail, it could change the dynamic of the relationships within the guild. For example, Gray, who has a complex relationship with Juvia, would surely be affected. Natsu, who is close to Lucy, might go on a quest to find her. Also, the guild's reputation could take a hit. Other guilds might see Fairy Tail as a place where members don't stay, which could affect future alliances and interactions.
One possibility is that the guild would experience a significant emotional impact. Lucy is a central figure, and her celestial spirit magic has been crucial in many battles. Juvia, with her water magic, is also a strong member. Their departure might lead to a decrease in the guild's overall power. Some members might feel betrayed, while others could be motivated to find out why they left and try to bring them back.
A possible reason could be personal conflicts within the guild. Lucy might have an issue with some of the guild's rules or how certain things are run. Juvia could be following Lucy for some reason, like loyalty or because she also has her own issues with the guild. For instance, if there are tensions between Juvia and other members over Gray.
In some fanfictions, Juvia and Lucy could be in a situation where they have to rescue a kidnapped guild member. Juvia uses her water magic to track the kidnapper's location through the moisture in the air. Lucy uses her keys to call upon spirits that can help in combat and stealth. Along the way, they face many challenges and have heart - to - heart conversations. This experience deepens their friendship and they become closer allies within the Fairy Tail guild.
One possible plot could be that Lucy and Juvia leave Fairy Tail to go on a self - discovery journey. They might want to explore their individual magic powers more deeply without the constraints of the guild. Maybe they travel to different magical realms, meet new characters, and learn unique magic techniques that they can bring back to Fairy Tail later.
She might leave due to heartbreak. For example, if she felt that Gray didn't return her feelings in the way she hoped, she could decide to leave to get over him and start anew.
Maybe they leave because they want to search for answers about their pasts. Happy might want to know more about his origins, and Lucy could be seeking something related to her family's history.
Often, in fanfiction, a common plot is that Juvia and Lucy are paired up for a task. This forced proximity makes them learn about each other. Lucy might introduce Juvia to new ways of using magic in a more creative way, while Juvia shows Lucy how to be more in tune with her emotions. As they face difficulties together during the task, they build a bond of trust. This trust then evolves into a deep friendship where they are always there for each other, whether it's cheering each other on during a magic competition or comforting each other after a loss.
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.
A powerful magical being from another dimension could be the main antagonist. This being senses the departure of Lucy and Juvia from Fairy Tail and sees it as an opportunity to invade their world. It tries to stop the two girls from getting help or finding a way to stop it, as they are two of the most powerful mages outside of the guild protection now.
One possibility could be that they leave to seek greater magical power. Maybe they've heard of a mysterious land filled with powerful magic and they decide to embark on a journey together. They leave Fairy Tail behind in order to become stronger and return to protect their guild in a more powerful way.
Maybe there are some dark mages who are after the magic that Lucy and Levy possess. As they leave Fairy Tail, they lose the protection of the guild, and these dark mages could target them. They would be antagonists as they try to steal the girls' magic or harm them in some way.