One common theme is the exploration of their unspoken feelings. Often, in the series, their relationship is somewhat ambiguous, and fanfiction allows for that to be explored more deeply with the kiss as a climax of those pent - up emotions.
One common theme is the realization of hidden feelings. Usually, both Lucy and Natsu have been friends for a long time, but the kiss makes them aware of their deeper romantic feelings for each other.
One common theme is adventure. Since they are from the Fairy Tail guild which is all about going on quests, many fanfictions continue this trend. They go on new adventures together, facing powerful enemies and discovering new magic.
The theme of unrequited love can also be common in some 'lucy loves natsu fanfiction'. Maybe at the start, Natsu doesn't realize Lucy's feelings or is too focused on other things like his next adventure or his training. This creates a lot of tension and drama in the story, as Lucy tries to hide or express her feelings while Natsu is oblivious.
One common theme is romance. Since Natsu and Lucy have a great chemistry in the original series, in hotel fanfictions, the hotel setting often provides a more intimate and private space for their relationship to develop, like in 'A Romantic Hotel Retreat' where they finally confess their feelings in a cozy hotel room.
Power and growth is another theme. As they face challenges together, they become stronger both magically and as individuals. Their relationship also strengthens during these times. They rely on each other's powers and learn to work in harmony, which is often explored in fanfictions.
One common theme is the idea of forbidden love. Since they are comrades in their original story, a kiss between them can be seen as something that goes against the norm of their friendship. Another theme is the discovery of new feelings. They might suddenly realize their attraction during a moment of danger or when they see each other in a new light.
Love and friendship are common themes. Since they are both from the Fairy Tail guild, their friendship forms the basis of their relationship in the fanfiction. The kiss is often a way to show the evolution from friendship to love.
One common theme is the expression of long - hidden feelings. Usually, in the original story, their relationship is more of comradeship, and in fanfictions, it's about finally admitting and acting on those deeper emotions that lead to a kiss.
Often, the theme of redemption can be found. Maybe Natsu has made a mistake in the past regarding Lisanna, and the kiss is a symbol of his apology and new start. Also, themes of courage and finally expressing hidden feelings are common. They might have been secretly in love for a long time but were too afraid to act, and the kiss is the culmination of that pent - up emotion. It gives the characters a chance to be more vulnerable and grow in the story.
One common theme could be forbidden love. Maybe they are from different social groups or have some sort of obstacle in their relationship that makes their kiss all the more intense.