There's a possibility that the father is a character who has been with Lucy from the start of the quest but has been in disguise or hiding his true identity. They could have fallen in love during their journey, and the pregnancy is a natural result of their relationship. However, his identity is only revealed later in the fanfic, creating a plot twist.
It could be a heroic character she meets during her quest. Maybe a powerful wizard or a brave knight who has a brief but intense encounter with Lucy, leading to her pregnancy.
The fanfic might focus on the relationships around Lucy during her pregnancy in this 100 - year journey. Her friends or family could be helping her, or there could be some who oppose her due to the special circumstances of her pregnancy. For example, there could be a prophecy related to her unborn child that some want to prevent from coming true. Also, the passage of time during this 100 - year quest could have a profound impact on her pregnancy. She may experience different stages of the pregnancy in different historical or magical periods, which could bring about unique difficulties and growth for her character.
Gray could also be a possibility. He and Lucy have a friendly rivalry and there are moments where their relationship could be interpreted as having deeper feelings. It would be an interesting twist if Gray was the father, as it would change the dynamics between him, Natsu, and Lucy in the fanfic.
The father of the baby could be a major character. He could be a loving partner, or there could be some drama if he's not as committed as Lucy. Her best friend could also be in it. The best friend might be the one she confides in about all her pregnancy fears and joys.
The identity and background of Lucy's father were described differently in different documents. In document 1, Lucy's father was an employee of a fallout shelter company. He took Lucy away during a mission and became the manager of a fallout shelter. He had launched a nuclear bomb to destroy Shayin City and was taken away by Mrs. Flame for interrogation. In document 3, Lucy's father was Jorde Hartfilia, a wealthy businessman. However, after his wife passed away, his relationship with his daughter became bad, causing her to run away from home. In document 5, Lucy's father was a man who abandoned Lucy's youngest daughter in Ode to Joy 5 in order to remarry quickly. In other documents, Lucy's father's identity was not mentioned. In summary, there were different descriptions of Lucy's father's identity and background, and it was impossible to get an accurate answer.
A Natsu x Lucy pregnant fanfic could be full of heartwarming moments. Think about Natsu being overprotective of Lucy during her pregnancy. He'd probably be a bit clumsy at first, but his love for her would shine through. And Lucy would be the one trying to keep things in order while also dealing with her hormonal changes. It could also add a new dynamic to the Fairy Tail group as a whole.
It's quite possible that there is such a fanfiction. Fanfiction thrives on exploring different relationships and storylines that may not be part of the original canon. Given the popularity of the characters Lucy and Sting, some fans might have been inspired to write a story where Lucy is pregnant with Sting's child. You could also try reaching out to fellow fans on social media platforms dedicated to the relevant fandom to ask if they've come across such a fanfiction.
One idea could be that Lucy discovers she's pregnant during a difficult time in the magical world. Gray is initially shocked but then becomes very protective. They might face challenges from their guild mates who are worried about how this will affect their ability to go on missions.
It's highly likely that there exists a fanfic with a Nalu and Lucy pregnancy plot. Given the large number of fanfic writers and the popularity of the Nalu ship, many fans like to create alternate storylines for the characters. Some might be interested in exploring the idea of Lucy becoming pregnant, perhaps dealing with how Natsu and Lucy would handle the situation, their reactions, and how it would affect their relationship and the world of Fairy Tail around them.
One plot idea could be that a magic spell goes wrong and Lucy ends up pregnant. Natsu is initially shocked but then quickly embraces the idea of being a father. They then have to deal with the guild's reactions, some of which are positive and some negative.
Well, one possible plot could be about Lucy's journey through her pregnancy. Maybe it focuses on how she prepares for the baby, like decorating the nursery. It could also show her dealing with the physical and emotional changes. For example, she might be excited but also a bit scared at the same time.