One possible plot development could be that the guild members quickly realize Lucy is missing and start a search. Natsu, being her closest friend, might lead the charge. They could follow any clues left behind, like a piece of Lucy's clothing or a strange magical residue. Another development could be that the kidnappers demand a ransom from the guild in the form of a powerful magical item. The guild then has to decide whether to give in or find another way to rescue Lucy. Or perhaps Lucy manages to escape on her own using her Celestial Spirit powers. She could call upon one of her spirits, like Leo, to help her break free from her bonds and then find her way back to the guild while avoiding the kidnappers.
Well, in this kind of fanfiction, a plot development might be that the kidnapper is actually someone with a vendetta against Lucy's family. So while she's kidnapped, she starts to learn more about her family's past that she didn't know before. Maybe there are secrets about her family's magic that the kidnapper wants to use for their own gain. As for her rescue, Gray could come up with a plan to infiltrate the kidnapper's lair. He could use his ice - make magic to create distractions and get to Lucy. Also, Erza might bring in some of her strategic skills to lead the rescue operation and ensure everyone is coordinated.
Well, one possible plot development could be that the kidnappers demand a ransom from Batman. Batman then has to race against time to find Robin without alerting the media or causing panic in Gotham. Another development might be that Robin manages to leave some hidden clues for Batman to find while being held captive. Maybe he uses his martial arts skills to briefly overpower one of the kidnappers and mark a symbol on the wall that only Batman would understand.
One possible plot development could be that his friends immediately launch a rescue mission. They might use their unique skills and resources to track down the kidnappers. For example, if Obi - Wan is involved, he could use his Jedi mind tricks to interrogate possible informants in the underworld.
She might use her celestial spirits in unexpected ways against the guild. For example, she could have her spirits create illusions to embarrass the members.
One possible plot development could be that Duke's friends in the Bat - family immediately start a search operation. They might use their various skills and resources to track down the kidnappers. For example, Batman could analyze the crime scene for any clues while Robin tries to hack into security cameras in the area.
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.
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.
Yes, there are likely fanfictions with such a plot. Fanfiction often explores different scenarios and relationships within the 'Fairy Tail' universe. However, not all of them are well - written or in line with the original spirit of the series.
Another scenario could be a misunderstanding within the guild. Maybe a new member misinterprets Lucy's actions as a threat and attacks her. In the heat of the moment, before the situation is clarified, Lucy gets beat up. This could lead to a story arc about resolving misunderstandings and building trust within the guild.
One possible plot development is that Natsu, as END, could be hunted by various magical organizations who see him as a threat. This would put him on the run and force his Fairy Tail friends to either protect him or try to stop him if they believe he's too dangerous. Another development could be that Natsu discovers new abilities related to END that give him an edge in battles but also come with a cost, like draining his life force or affecting his mental state.
One possible plot development could be that Natsu discovers a new and powerful magic during his return that gives him an edge in saving Fairy Tail. Maybe he finds a way to combine his Fire Dragon Slayer magic with some ancient magic he stumbles upon on his journey back.