One possibility is that Lucy discovers a hidden power within herself that is related to dragon slaying. Maybe she has a long - lost ancestor who was a dragon slayer. This newfound power could lead her on a journey to learn more about it, facing challenges along the way, like dealing with other mages who are jealous or scared of her new abilities.
Perhaps the story could start with Lucy being in a situation where she has no choice but to learn dragon slaying skills. For example, a powerful dragon is threatening the guild she belongs to. She decides to study the art of dragon slaying to protect her friends. Along the way, she could also form alliances with other characters from the original series who are interested in helping her in her new endeavor.
Well, it could start with Lucy being in a situation where she witnesses the destruction caused by a celestial dragon. This event stirs something deep within her, and she decides she wants to be able to protect everyone from such a threat. So, she embarks on a journey to become a celestial dragon slayer. She may travel to different realms or seek out rare magical items that can enhance her abilities. As she progresses, she could form alliances with other powerful mages who share her goal or have knowledge about celestial dragons. And gradually, she builds her skills and reputation as a celestial dragon slayer.
In a 'Fairy Tail Lucy becomes a Dragon Slayer' fanfic, it could start with Lucy being in a life - threatening situation. To survive, she unknowingly absorbs the power of a dying dragon. This power starts to change her. At first, she is scared of the changes. But then, with the support of her friends, she decides to embrace it. She then begins a journey to master her new powers. She might learn that her Dragon Slayer magic is linked to a special type of celestial spirit that has dragon - like qualities, and she has to find and bond with this spirit to fully control her powers.
Well, it could involve Issei discovering some ancient dragon magic. Maybe he stumbles upon a dragon's lair and is blessed with dragon powers. He might start to have dragon - like instincts, like a strong urge to hoard treasures or protect a certain territory.
The plot might start with Hiccup having a strange encounter, like stumbling upon a hidden cave with a magical artifact. This artifact could be the key to his transformation into a dragon god. As he becomes more dragon - like in his powers, he could gain the ability to communicate with dragons on a whole new level, understanding their deepest thoughts and feelings. And he would surely have to use these powers to protect Berk from threats that normal human - dragon alliances couldn't handle.
Perhaps an ancient sorcerer who has the ability to control celestial dragons. He sees Lucy as an obstacle to his domination over the world using the power of these dragons. He would use his vast knowledge of magic and his control over the dragons to try and defeat her.
Maybe Lucy has a secret power that helps her in slaying dragons. She could be on a quest to save her world from dragon - related threats while keeping her power a secret from her friends at first.
Her relationship with Natsu would likely change significantly. Since Natsu is a dragon slayer, they might become rivals in a friendly way, constantly trying to outdo each other in terms of dragon slaying skills. But they could also team up more often, combining their unique abilities to face greater threats.
The plot could involve Naruto somehow getting cursed by Slenderman. This curse starts to affect his ninja abilities, like his chakra control. As he tries to figure out what's wrong, he discovers the connection to Slenderman. He then has to journey into the dark and mysterious places where Slenderman lurks to break the curse. Along the way, he might meet some of Slenderman's minions and have to fight them using his unique jutsu.
Well, in a Naruto becomes a hollow fanfiction, perhaps the chakra system in Naruto gets corrupted and turns him into a hollow. His appearance would change to something more menacing. He might start to crave spiritual energy instead of normal food. His relationships with other characters would be on edge. For example, his bond with his teacher Kakashi would be tested as Kakashi tries to figure out how to reverse the transformation or at least help Naruto co - exist with his new hollow self.
In a Naruto - becomes - a - teacher fanfiction, Naruto could focus on teaching his students about the value of friendship and teamwork. He might organize team - building exercises that are actually dangerous ninja missions. His students would learn to rely on each other, just as he did with his own team. He could also share stories about his adventures with the Akatsuki, making sure his students understand the threats that still exist in the ninja world.