One idea could be that Lucy pranks Natsu by using her Celestial Spirits to create fake fire-breathing dragons all around the guild. Natsu gets excited at first, thinking there are real dragons, and tries to fight them. When he realizes it's a prank, he's both annoyed and impressed by Lucy's creativity.
Lucy might prank Gray by magically changing all his clothes into different, outlandish styles every time he tries to strip. So instead of his normal underwear or lack thereof, he ends up in a frilly pink dress or a clown suit. This would be a hilarious prank considering Gray's habit of accidentally undressing.
In some fanfictions, Lucy pranks Erza by making her think that there's a new rule in the guild about eating only sweet things. Erza, being strict about rules, starts to enforce it until she realizes it was a prank. It's memorable because of Erza's initial seriousness.
Perhaps a time - traveling adventure where Lucy is sent back to the day she first joined Fairy Tail on her birthday. She gets to relive those memories and also make some changes that end up strengthening the bonds within the guild even more.
One idea could be a crossover where Naruto and Lucy team up to fight a common enemy. Maybe a powerful dark mage from Fairy Tail's world has somehow made its way into the Naruto universe and is causing chaos. Naruto's ninja skills combined with Lucy's celestial spirit magic would make for an exciting battle.
One idea could be a story where Jackal and Lucy are forced to team up during a mission. Maybe they start off not getting along but gradually learn to respect each other's skills. For example, Jackal's combat abilities combined with Lucy's celestial spirit magic could make for some really cool battle scenes against a powerful enemy.
A plot could involve Freed accidentally casting a spell that links his and Lucy's minds. At first, it's a chaotic mess as they have to deal with suddenly sharing thoughts and feelings. But as time goes on, they start to understand each other on a deeper level. They use this newfound connection to uncover a plot within the Fairy Tail guild by a group of mages who are trying to undermine the guild's leadership, and in the process, their relationship blossoms.
One plot idea could be that Lucy discovers a cat with magical powers that is related to an ancient Fairy Tail legend. The cat could lead her on a quest to find a hidden treasure that was lost long ago in the world of Fairy Tail.
One idea could be that Lucy discovers she has hidden witch powers passed down through her family. Maybe she can use these powers to save the Fairy Tail guild from a new, powerful dark magic threat. Another plot could involve Lucy being transported to a parallel world where she is a well - known and feared witch, and she has to find her way back while also learning about her new - found powers in that world.
One plot idea could be that Hibiki and Lucy are on a joint mission. They discover an ancient magic artifact that has the power to either save or destroy the world. Along the way, they face various challenges and their friendship grows as they rely on each other's unique magical abilities to overcome obstacles.
One plot idea could be that Lucy and Lisanna team up for a special S - class mission. They face a powerful dark wizard who has the ability to control time. Along the way, they discover new magic spells and also learn more about each other's pasts. This would create a lot of action and character development.
One idea could be that while drunk, Lucy accidentally casts a powerful but misdirected spell that creates chaos in the guild hall. All the guild members then have to work together to reverse the spell's effects. It could lead to some really funny and heartwarming moments as they deal with a very tipsy Lucy and the mess she's made.