One common theme could be the challenges they face as they prepare for parenthood. It might involve things like how they adjust their lives in the Fairy Tail guild with a baby on the way.
One challenge could be the physical changes Mirajane experiences. It might limit her ability to use her magic or participate in guild activities for a while. Another challenge is the fear of the unknown, especially for Laxus who might worry about being a good father.
I'm sorry, I don't have specific fanfic stories to recommend directly. You can try searching on popular fanfic platforms like FanFiction.net or Archive of Our Own. There you can use the search terms 'laxus and mirajane pregnant' to find relevant stories.
A Rated M fanfic involving Laxus and Mirajane with teenagers could explore complex themes. Maybe it shows how the older characters like Laxus and Mirajane interact with the younger generation of teenagers in the context of the Fairy Tail world. It might deal with issues such as mentoring or protecting the teenagers from various threats in their fictional universe.
You can expect a lot of character development. Laxus might show his tough yet caring side, Mirajane could display her strength and femininity, and Lemon (if it's an original character) would have their own distinct traits. There could be some epic battles where they use their magic powers in unison.
I'm not sure of a specific one titled exactly like that, but you could look for fanfics on platforms like FanFiction.net or Archive of Our Own. Search for stories that involve all three characters. You might find some where Laxus and Mirajane have to team up with Lemon for a special mission in the magical world they inhabit. It could explore their different personalities and how they work together.
Their relationship could become more tender. Laxus, who is often seen as tough, might become more protective of Mirajane. For example, he would not let her take on dangerous missions anymore.
Laxus might become more tender and less brash. His focus would shift from just being a strong mage in the guild to being a father. Mirajane, on the other hand, would likely become even more nurturing. She already has a motherly side, but this would be amplified.
One idea could be focusing on how their guild mates react. Maybe there could be a big celebration in the guild hall, with everyone bringing gifts and sharing their excitement. Another plot could revolve around their preparations for the baby, like choosing a name or decorating the nursery.
One possible aspect of a Mirajane and Laxus fanfiction could be their friendship development. They could start off as comrades in their guild, Fairy Tail. Maybe they are paired up for a difficult mission, and during that time, they learn to rely on each other's unique skills. Mirajane's charm and her ability to transform could be a great asset, while Laxus's raw power and leadership skills would also play a crucial role.