I'm not entirely sure if there is a specific 'natsu and mirajane pregnant fanfic'. Fanfic availability can vary greatly. Some fanfic authors might have explored this idea, while others may not. You could also try reaching out to fanfic communities on social media platforms and ask if anyone knows of such a fanfic.
It could be a story full of emotions. There would likely be a lot of anticipation and excitement. Natsu might be protective and a bit clumsy in his attempts to take care of Mirajane. And Mirajane would probably be strong yet vulnerable at the same time, dealing with the changes in her body and the new life growing inside her.
Well, there could be such a fanfiction out there. However, it really depends on the creativity and interests of the fanfiction writers in the relevant fandom. Some might find this concept interesting to write about, while others may not. It also might not be very common as it involves a rather specific and perhaps controversial plot point in the context of the characters.
Erza would probably be very protective. She would make sure Mirajane is taking proper care of herself and would offer practical advice on things like diet and exercise during pregnancy. Gray might be a bit awkward at first but would warm up and offer to help with any heavy lifting or tasks around their home.
Some alternatives could involve fanfictions centered around their individual character development. For example, a fanfiction about Natsu learning a new powerful spell or Mirajane exploring a new side of her magic. There could also be stories that place them in different settings, like a modern - day AU (alternate universe) where they are just regular people dealing with normal life problems while still maintaining their core character traits.
There might be a fanfiction where the pregnancy is a surprise to both. For example, in a story called 'Unexpected Miracles', it could start with Mirajane realizing she's pregnant and then Natsu's reaction being a mix of shock and joy. They then have to deal with the challenges of impending parenthood in a world full of magic and danger.
A plot could be that during a difficult mission, Mirajane discovers she's pregnant. Natsu then has to balance protecting her and completing the mission. This would add a layer of tension and emotion to the story.
A great Natsu x Mirajane fanfic often has well - developed characters. It should stay true to the personalities of Natsu and Mirajane from the original Fairy Tail series. For example, Natsu's impulsiveness and love for fighting, and Mirajane's kind yet powerful nature.
Their relationship would likely become more intimate and deeper. With a baby on the way, they'd have to rely on each other more. Natsu would probably become more gentle and caring towards Mirajane, and Mirajane would feel more protected by Natsu.
The popularity of 'Fairy Tail Natsu x Mirajane fanfic' comes from the fact that both characters are very popular in the 'Fairy Tail' series. Fans like to explore different relationships between the characters, and Natsu and Mirajane have very distinct personalities that can create interesting dynamics.