Avoiding the 'lemon' aspect which is not suitable for general discussion, in 'nalu police' fanfiction, there can be themes of mystery and adventure. They could be investigating a series of strange crimes in the city. Their different personalities, Natsu's impulsiveness and Lucy's rationality, would play a role in how they approach the cases. Also, there might be a theme of self - discovery as they face challenges in the police world and learn more about themselves and each other.
I can't really focus on the 'lemon' part as it may involve adult - oriented themes. For the 'nalu police' part, often you'll see themes like justice and protection. Natsu and Lucy might be involved in chasing down bad guys, and in the process, their bond as partners (and potentially more) grows. There could also be themes of loyalty, not just to each other but also to the police force they belong to.
Another theme might be the unexpected situations that occur due to their drunken state. For example, they could end up in a place they've never been before or get involved in some comical misunderstandings. Also, the 'lemon' aspect might imply a bit of a more mature exploration of their relationship, like a new level of physical closeness or attraction that is explored in a tasteful way in the story.
One common theme could be young love. Since it's set in highschool, Nalu's relationship would be in its budding stage. Another theme might be friendship groups and how they influence Nalu's relationship.
One common theme could be the development of an unexpected relationship. For example, in a Nalu teacher - themed fanfiction, there might be the exploration of how Natsu and Lucy, if in a teacher - student type of dynamic (even if not traditional in a sense), grow closer. Another theme could be the over - coming of obstacles. Maybe there are rules against their relationship in the story's setting, and they have to fight against those. Also, self - discovery can be a theme, as they learn more about themselves through their interactions with each other.
A common theme is the magic of Christmas combined with their love. The Christmas setting can create a more romantic and cozy atmosphere for Nalu. The lemon aspect might bring in some elements of their more private and passionate side. For example, they could have a private Christmas dinner and then some tender moments that are a bit more on the steamy side. There could also be themes related to hope and new beginnings, as Christmas is often seen as a time for that, and their relationship could be evolving in that context.
One common theme could be the exploration of the passionate relationship between Natsu and Lucy. Since it's 'rough lemon', there might be a focus on more intense physical interactions within their relationship.
The theme of redemption can also be found in some police officer lemon fanfiction. Maybe a police officer has made a mistake in the past, either in their personal or professional life, and through their relationships and new experiences in the story, they seek to make amends. This adds depth to the character and the overall story.
The anticipation of the new life is another theme. Writers often describe how they both look forward to the arrival of their baby. They might dream about the baby's future or argue about baby names.
One common theme is domestic bliss. Writers often explore how Natsu and Lucy create a warm and loving home together. For example, they might show Natsu bringing home little trinkets for Lucy or Lucy cooking a special meal for Natsu.
One common theme is the struggle between Natsu's vampiric nature and his love for Lucy. His vampiric instincts might drive him to do things that could potentially harm Lucy, and he has to constantly fight against that. Another theme could be the mystery surrounding his transformation into a vampire. Fans often write about how it happened and what it means for his place in the Fairy Tail guild.
One common theme is the clash of different power systems. Since Nalu comes from Fairy Tail with magic and Naruto has ninja abilities, seeing how they interact and compare is often explored.