Well, obviously she'll interact with her past self. It would be really interesting to see how she reacts to seeing a younger and more naive version of herself. She could also meet characters who are no longer alive in the present. For example, if there were any great wizards from the past who played important roles in the history of magic. Additionally, she might cross paths with some of the villains from the past who were causing trouble long before the current villains in the story. This could change her perspective on the whole conflict in the present.
In this fanfiction, Lucy would surely interact with her family's servants or associates from the past. They might know some secrets about her family that she is not aware of in the present. She may also encounter some of the magic council members from the past who had different policies and attitudes. And of course, there could be some new characters that are unique to the past time period, like local mages who were not mentioned in the main story but have their own significance in the past world that Lucy now finds herself in.
Death the Kid would be an extremely interesting character for Lucy to interact with. His obsession with symmetry and his powerful abilities as a meister could lead to some really unique scenarios. Lucy might be both fascinated and a bit put off by his quirks at first. But as they get to know each other, they could learn a great deal from one another. For example, Death the Kid could help Lucy understand the importance of precision in combat, which could enhance her use of celestial spirit magic, while Lucy could introduce him to the concept of celestial spirits and their different powers.
Naruto would probably be very enthusiastic and friendly towards Lucy. He'd be curious about her magic. Lucy might be a bit cautious at first but would soon warm up to Naruto's positive energy. They'd likely share stories about their adventures and friends.
One interesting plot twist could be that when Lucy goes back in time, she discovers that her family has a much darker secret than she ever knew. Maybe they were involved in some sort of magic that was considered forbidden in the past. Another could be that she accidentally changes the future in a way she didn't expect, like making her friends not become the people she knew them as. And perhaps she finds out that an enemy in the present was actually once an ally in the past, and she has to figure out what went wrong to turn them into an enemy.
Natsu is often paired with Lucy. Their chemistry in the original series makes it a popular choice in fanfiction. Gray might also be paired with her in some stories, as their interactions can be explored in a more adult way.
This could be an interesting fanfiction concept. Naruto's energetic and determined personality would contrast with Lucy's more elegant and sometimes sassy nature. Maybe Naruto could use his ninja skills to protect Lucy in the Fairy Tail world, adding a whole new dynamic to the story.
There's also 'Lucy's New Beginnings'. This one is about male Lucy starting his journey in the magical world in a completely different way than in the original story. He meets different characters first and forms unique alliances. It's a long - form fanfiction that really develops his character well.
One great 'Lucy Heartfilia hurt' fanfiction is 'Bleeding Heart'. In this story, Lucy gets injured during a battle with a powerful dark wizard. The author does a wonderful job of portraying her pain and the concern of her guild mates. It really delves into her character and shows her strength even when she's physically and emotionally hurt.
Erza Scarlet frequently appears as a supporting character. She is strong and strict, which can push Lucy to become better. Her combat skills and leadership qualities are valuable assets in the fanfiction. Wendy Marvell can be a supporting character too. Her healing magic can be crucial in keeping the team, including Lucy, in good shape during their adventures. And of course, Levy McGarden, as Lucy's friend, is often there to offer her knowledge of books and magic, which can be really helpful when they are dealing with the mysteries in the game world.
She could use her celestial keys to open portals to different islands in the One Piece world. This would be a really cool way to travel and could also lead to some interesting encounters. For instance, she might end up on an island full of devil fruit users and have to use her magic to survive.
In a fanfiction, Lucy might be a new addition to the Grand Line. She could bring a different kind of power dynamic. Her magic could be seen as a rare and valuable asset. The Straw Hats might initially be skeptical of her, but as they see her power in action, they welcome her into the crew. And she could learn from the different fighting styles in One Piece, like Luffy's Gum - Gum attacks.