One way it could end is with a big showdown. The Fairy Tail guild members find the kidnappers' lair, and there's an epic battle. Natsu defeats the main kidnapper with his powerful fire magic, and Lucy is freed. Then they all return to the guild, where there's a big celebration.
The fanfiction could end on a more emotional note. Maybe during her captivity, Lucy discovers something about herself or her relationships. When she's finally rescued, she has a heart - to - heart with Natsu or another member about how this experience has changed her. And the guild becomes even more united in protecting each other. So it ends with a sense of growth and unity within the guild.
In a fanfiction where Lucy is kidnapped, the Fairy Tail guild would likely spring into action. Natsu, being her closest friend, would be furious and determined to find her. He'd probably charge off without much of a plan, with Happy flying after him trying to keep him in check. Gray would also be involved, using his ice - magic to combat any obstacles in their way. Erza would lead the strategic part of the rescue mission, planning their every move carefully.
In some fanfictions, if Natsu kidnapped Lucy, it could be a comical situation. Natsu might do it out of his own strange sense of protecting Lucy in an overzealous way. Maybe he thinks there's a danger that only he can keep her safe from, and his impulsive nature leads him to this 'kidnapping' which is more like a forced protection.
Her relationship with Natsu would likely change. Natsu might be initially distrustful of Lucy if he senses her connection to End, since End is often seen as an enemy. But then as he realizes that Lucy is still the same person deep down, their bond could become even stronger as he helps her control this new aspect of herself.
One potential kidnapper could be a dark wizard who wants to use Lucy's Celestial Spirit keys for their own dark magic. Another could be a rival guild member who is jealous of Lucy's power and wants to steal her keys to gain an advantage in the magical world. It could also be someone from Lucy's past, like an old acquaintance who has turned bad and has some grudge against her.
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.
The plot could revolve around a dream sequence. Lucy dreams that she is in a vulnerable state, like being naked, which symbolizes her insecurities. In the dream, she has to face her fears and overcome them, perhaps with the help of her Fairy Tail comrades. This would be a way to explore her character on a deeper level without being inappropriate.
One interesting plot twist could be that Lucy discovers a hidden power within herself that is linked to End. Maybe she can control a part of End's power and use it to save the Fairy Tail guild from a great danger. For example, she might be able to use it to stop an ancient evil that is more powerful than any they've faced before.
One possible fanfiction could be that Lucy is invited to a grand ball in the magical world. As she enters the ballroom, a mysterious melody starts playing. Lucy, being the confident and graceful character she is, starts to dance. Her celestial spirits watch in awe as she twirls around, her dress flowing with each movement. It could be a dance that not only showcases her beauty but also her connection to the magic within her, as she uses a bit of her magic to create a sparkling effect around her while she dances.
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.
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.