It could be one of her close friends from the guild. Maybe Jellal, considering their complex relationship in the original story. There's already a lot of history between them, and this could be a new development in their relationship.
Another possibility is a new character introduced just for this fanfiction. This new character could be a powerful wizard from another land who Erza meets during a mission. They have a brief but intense encounter, and he ends up being the father. It would add a whole new layer of drama and mystery to the story.
It could be a long - time boyfriend that we haven't known much about in the original story. Maybe he's a character who was in the background but now becomes central to the plot.
There's also a chance that it could be a god in disguise. Gods have been known to have relationships with mortals and demigods. So perhaps a god took on a human form and had a relationship with Thalia, resulting in the pregnancy.
It could be her existing partner from the original story. For example, if it's a story where she's in a relationship with Edward, then he would be the likely father.
There could be such a fanfiction. Fanfiction writers often come up with all kinds of creative and sometimes out - of - the - box ideas. However, I haven't personally come across one where Natsu gets Erza pregnant. It might be a rather niche concept within the Fairy Tail fanfiction community, as most fanfictions tend to focus on different aspects of the characters' relationships, like friendship, adventure - related partnerships, or other forms of romantic development.
In Erza's world, there could be a dark mage who wants to use the power of the unborn child for their own evil purposes. They might see the combination of Naruto's ninja abilities and Erza's magic in the child as a great source of power and will stop at nothing to get their hands on it.
It could be Michael. Since they have a complex relationship in the Roswell series, it's possible that their relationship takes a new turn and he is the father. Maybe they had a passionate night together that led to the pregnancy.
One possible plot could be that Erza discovers she's pregnant and has to deal with the shock while still being part of her guild and its adventures. She might worry about how it will affect her ability to fight and protect her friends.
Yes, there could be. Some fanfiction writers are creative enough to come up with a story where Naruto and Erza interact in a way that is suitable for all ages. For example, they might be in a shared adventure in a new world where some strange magic or power causes a false pregnancy - like situation as part of the plot mystery, rather than anything inappropriate.
There might be such fanfictions in the vast world of Fairy Tail fanfiction, but I haven't specifically come across one. Fanfiction often explores various relationships and scenarios that are not part of the original canon, so it's possible for creative fans to write such a plot.
Another option could be a mysterious figure. For example, a character from another dimension or a new character introduced specifically for this plot twist. This could add an element of mystery and intrigue to the story.