One way to develop Lucy's character is through her adaptability to the new form. She might face difficulties at first, like not being able to control her new powers properly. But as she overcomes these challenges, she becomes more mature and capable. Also, her interactions with other Fairy Tail members in her transformed state can reveal different aspects of her character, such as her loyalty, kindness, and determination.
One popular plot idea could be Lucy unlocking a new and powerful transformation during a life - or - death battle. Maybe she discovers a hidden celestial spirit magic within her that changes her appearance and gives her enhanced powers. For example, she could transform into a being that can control multiple celestial spirits at once, something not seen before in the Fairy Tail universe.
In many fanfictions, Future Lucy starts off as a determined and somewhat broken character. She has seen the destruction of her world and is desperate to change it. As the story progresses, she learns to trust the people in the past. For example, she might initially be hesitant to work with Natsu and the others, but as she sees their kindness and determination, she becomes more open. This helps her character grow from a lone wolf trying to save the world to someone who is part of a team.
Lucy would likely become more independent. In high school, she'd face new challenges without her usual Fairy Tail comrades always by her side. This would force her to rely on her own wits and celestial spirit powers more often.
To develop their relationship, start with small interactions. Have the OC offer to help Lucy with her celestial spirit summoning, like finding a rare ingredient for a spirit - summoning spell. Then, they could have some shared experiences, such as getting trapped in a cave during a mission. This forces them to rely on each other, talk, and get to know one another better. Another way is to give them common goals. For example, they both want to defeat a certain dark mage who has been causing trouble in the area. Working towards this goal together will bring them closer.
To develop Lucy's child character, start with their magic. If they inherit celestial spirit magic, show how they learn to summon and communicate with the spirits. Also, consider their personality. They could be brave like Natsu, or more calm and collected like Gray. Their relationships are important too. How they interact with the older Fairy Tail members can shape their character. For example, if they look up to Erza, they might learn about discipline from her.
Their relationship could start with mutual suspicion. Lucy is a member of Fairy Tail, and Midnight is from a different, often opposing group. But as they interact more, they might find common interests. For instance, they could both be interested in a particular type of magic theory. This shared interest could be the starting point of them gradually warming up to each other.
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.
She would probably be more innocent and naive at first. But as she experiences the adventures and challenges in Fairy Tail, she would gradually become more confident and brave. For example, facing her first real battle might be terrifying, but it would also be a huge step in her growth.
Their relationship could develop through shared experiences. For instance, if they both get caught in a magical trap that only they can escape from by working together. They would have to rely on each other's skills, and this could lead to a newfound respect. Jackal might see Lucy's intelligence in figuring out the magic of the trap, and Lucy could see Jackal's tenacity.
In a fanfiction, their relationship might develop because of a mutual friend. Maybe a character from Fairy Tail is in danger and they both care about that person. So they work together to rescue the friend. During this rescue mission, they see different sides of each other. Angel might see Lucy's determination and kindness, and Lucy might see Angel's hidden strengths and softer side. This new understanding can lead to a closer relationship between them.