Perhaps her father is an OC dragon slayer. He saved Lucy's mother from a dragon attack long ago. They fell in love, but he had to go on a long - term mission. During this time, Lucy was born. Years later, when Lucy discovers her father's identity, she also learns that she has some latent dragon slayer abilities passed down from him. This could open up a whole new arc in the fanfic about her exploring these new powers.
A great storyline could be that her real father is an OC time - traveling mage. He accidentally travels to the future and falls in love with Lucy's mother. But then he gets trapped in the future and has to watch his daughter grow up from afar. This could lead to some really emotional scenes when they finally meet.
One interesting storyline could be that Lucy's real father is an OC celestial spirit. He took on a human form to be with Lucy's mother. But there were rules against celestial spirits having relationships with humans. When Lucy was born, he was punished and sent back to the celestial world. In the fanfic, Lucy could find a way to communicate with him through her celestial keys and learn about her true origins and the secrets of the celestial world from him.
It could be an OC nobleman. In the fanfic, perhaps he met Lucy's mother at a grand ball. He might have had a brief but passionate relationship with her. However, he was forced to abandon her due to family or political pressures. This would add a lot of drama to the fanfic, especially if Lucy discovers her true heritage later on and has to face the consequences of her father's actions.
One great story could be 'The OC's Adventure with Lucy'. In it, the original character has a unique magic that complements Lucy's celestial magic. They go on a quest to find a lost celestial key, facing various challenges along the way. It's full of action and the developing relationship between the OC and Lucy is really interesting.
Another theme is the exploration of magic. Lucy has her celestial magic, and the OC usually has some form of unique magic as well. The fanfictions often explore how their different magics can work together or clash. It's interesting to see how the authors play with the magic system in the Fairy Tail universe to create new and exciting storylines for Lucy and the OC.
Natsu is a very likely candidate. Their relationship in the original series is quite close and has a lot of potential for a romantic sub - plot that could lead to him being the father. Their chemistry would make for an interesting story as they navigate parenthood.
A third theme is self - discovery. Her anger makes her re - evaluate who she is and what she's capable of. This can lead to her exploring different aspects of her magic, her relationships, and her place in the guild or the magical world at large. It's a way for the authors to show Lucy growing and evolving as a character.
Death the Kid would be an extremely interesting character for Lucy to interact with. His obsession with symmetry and his powerful abilities as a meister could lead to some really unique scenarios. Lucy might be both fascinated and a bit put off by his quirks at first. But as they get to know each other, they could learn a great deal from one another. For example, Death the Kid could help Lucy understand the importance of precision in combat, which could enhance her use of celestial spirit magic, while Lucy could introduce him to the concept of celestial spirits and their different powers.
One idea could be exploring how Lucy's pregnancy affects her magic. Maybe she discovers new powers or has to adapt her existing ones. Another plot could focus on the reactions of her friends in the guild. They might be overjoyed and very protective. Also, a story could be written about how she prepares for the baby's arrival while still dealing with any threats to the guild or the magical world.
One possible plot could be that Naruto is somehow transported to the Fairy Tail world where he meets Lucy Heartfilia. They could team up to fight a common enemy that threatens both their worlds. Naruto's unique ninja skills combined with Lucy's celestial spirit magic would make for some epic battles.
Yes, there are quite a few out there. You can start by looking on popular fanfic websites like Archive of Our Own. Just search for 'luffy x lucy heartfilia' and you'll find a variety of stories with different plotlines and writing styles.
Another fanfic could focus on Lucy's relationship with Erza. Maybe they team up for a tournament within the Fairy Tail guild. Along the way, they face tough opponents and have to rely on each other's strengths. Lucy's strategic thinking combined with Erza's powerful combat skills would make for an exciting story.