One great fanfiction is 'A New Adventure'. It shows Lucy in a whole new adventure where she discovers a hidden magic. The story has great character development for Lucy and interesting plot twists.
Another fanfic could focus on Lucy's relationship with Erza. Maybe they team up for a tournament within the Fairy Tail guild. Along the way, they face tough opponents and have to rely on each other's strengths. Lucy's strategic thinking combined with Erza's powerful combat skills would make for an exciting story.
A good one should have strong character portrayal of Lucy. For example, it should capture her determination and kind heart. If it can show her growth as a wizard, that's even better.
In some fanfictions, Lucy's departure from Fairy Tail could be part of a self - discovery arc. She could feel that she has outgrown the guild in a way, or that she needs to explore the world on her own terms. So she leaves, travels to different places, studies different forms of magic, and then returns to Fairy Tail as a much more powerful and confident mage, ready to contribute even more to the guild.
Some writers portray it as a very emotional event. Lucy might be shown as heartbroken but determined as she walks away from the guild she loves. Her friends are often shown as being in shock or trying to persuade her to stay.
A great plot twist could be that one of the Fairy Tail guys, like Loke, is actually a double agent working for an enemy guild. Lucy discovers this and has to decide whether to trust him again or turn him in. It would create a lot of internal conflict for her.
One great Layla Heartfilia fanfiction could be about her early adventures in the Fairy Tail world that haven't been fully explored in the original series. Maybe it delves into her relationships with other guild members before they were as well - known as they are now.
Erza might see it as a sign of Lucy growing up and becoming more independent. She could view it as a mark of Lucy's determination and might even be a bit envious of Lucy's newfound self - expression. This could lead to some interesting conversations between them about self - identity and how they each represent Fairy Tail.
If Lucy never joined Fairy Tail, the friendships and relationships among the characters would form in a very different way. Also, many of the story arcs might not unfold as they do in the original plot.
One great Anna Heartfilia fanfiction is 'Anna's Legacy'. It delves into her backstory and her connection to the Heartfilia family magic. The story has some really cool moments where Anna's strength and wisdom are showcased, and it ties in well with the overall Fairy Tail lore.