It could be that there are some internal issues within Fairy Tail that make her leave while being pregnant. For example, there might be a prophecy or a curse that she believes could harm her baby if she stays. So, in order to break free from that potential threat, she decides to leave. Also, she may be facing some personal conflicts with other members of Fairy Tail regarding her pregnancy, like some not being supportive or having different views on how she should handle it, which ultimately drives her to leave.
One possible plot could be that Lucy and Juvia leave Fairy Tail to go on a self - discovery journey. They might want to explore their individual magic powers more deeply without the constraints of the guild. Maybe they travel to different magical realms, meet new characters, and learn unique magic techniques that they can bring back to Fairy Tail later.
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.
It could be a new character introduced specifically for the fanfiction. Maybe a powerful mage who has a vendetta against Lucy and somehow manages to drive her out of Fairy Tail by causing trouble for her within the guild.
Well, one possible plot could be that Lucy has to face the challenges of pregnancy alone after Natsu leaves. She might struggle with financial difficulties and the emotional turmoil of raising a child without the father. She could then find support in her friends in the guild, who help her through the tough times and she eventually becomes a strong, independent mother.
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.
Perhaps Naruto is on a quest to find a way back to his own world. He realizes that staying in Fairy Tail is only delaying his journey. He has a sense of loyalty to his own friends back home like Sasuke and Sakura. So he leaves Fairy Tail, even though he has made some friends there, in order to pursue his ultimate goal of returning to Konoha.
Maybe the story could focus on Lucy's journey during the pregnancy. She could be dealing with morning sickness and hormonal changes while Gray is away on some important mission. This could lead to some misunderstandings between them, but in the end, they come closer together when Gray realizes how much Lucy needs him.
A powerful magical being from another dimension could be the main antagonist. This being senses the departure of Lucy and Juvia from Fairy Tail and sees it as an opportunity to invade their world. It tries to stop the two girls from getting help or finding a way to stop it, as they are two of the most powerful mages outside of the guild protection now.
It could be that Lucy leaves Fairy Tail because of a personal quest she has to undertake. This quest might be related to her family or her past, and she feels that she has to do it alone without the support or interference of the guild. She may plan to return once she has completed this important task.
Perhaps Caroline initially struggles with the idea of being a single mother. She may consider reaching out to Klaus but then decides against it. As time passes, she discovers new powers within herself because of the pregnancy. These powers help her protect her unborn child from various threats that come her way, and she becomes a stronger and more independent character.