Well, it could be that Lucy has a hidden power linked to the origin of the celestial spirits. In fanfiction, authors might explore the idea that she has the ability to rewrite the rules governing the spirits. For example, she could potentially free them from their contracts while still maintaining a strong bond, and this new relationship could unlock a new level of power for both her and the spirits.
In some fanfictions, Lucy's true power might be related to her celestial spirit heritage in a deeper way. Maybe she can merge with her spirits on a more profound level, not just summoning them for combat. This could give her enhanced physical and magical abilities.
Perhaps it's a power related to the stars in a more direct way. Like she can draw energy from specific constellations and use it to enhance her attacks. For example, if she summons the power of Orion, she gets super strength and accuracy in her attacks.
Often, her true power is shown as an amplification of her celestial spirit magic. For instance, she might be able to call upon multiple spirits simultaneously without tiring, which is a significant upgrade from her normal abilities in the original series.
If Lucy gets a new power, it will likely change the power dynamics in the Fairy Tail guild. She might be able to take on tougher opponents on her own, which could lead to more solo missions for her.
Well, one possibility could be that the story focuses on how Lucy adjusts to her new state. Maybe she has to cut back on her guild missions at first. She might worry about how Natsu and the others will react. It could also involve her having strange pregnancy cravings that lead to some comical moments in the guild. And as her pregnancy progresses, she could start preparing a nursery in her home, all while still being part of the Fairy Tail family.
Maybe she just lost interest in the Fairy Tail world. Fanfiction can be a passing fancy, and her enthusiasm might have waned over time.
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.
Well, if we're following the common ships in the Fairy Tail fandom, Natsu could be a likely candidate. Their relationship is very close and there are many hints of a deeper connection between them in the original series. It would make for an interesting story as Natsu would have to grow up a bit to take on the role of a father.
In a fanfiction, there could be a situation where Lucy is forced to side with a group that Natsu is against. This would make Natsu see her as an enemy. Or perhaps there is a prophecy that Lucy is involved in that Natsu misinterprets as something bad. He might think she is a threat to the guild or his friends. Also, if there is a love triangle situation where Lucy chooses someone else over Natsu in a way that really hurts his feelings, that could be a reason for him to start hating her.
One idea could be that Jackal, after some soul - searching, decides to turn over a new leaf and teams up with Lucy. They could go on a mission to retrieve a powerful magical artifact that was once used by an ancient dark wizard. Along the way, Jackal's knowledge of the dark arts helps them navigate through various traps, while Lucy's celestial magic provides the offensive and defensive power they need.
Midnight might use his illusions to make Lucy think she's lost her Celestial Keys. This would be a huge psychological blow to her. But then Lucy could remember the bond she has with her spirits and break through the illusions. It would be a battle of wills as much as magic.