One common theme is friendship. Despite their differences, Nikki and Max often form a unique bond in these fanfictions. Another theme is adventure, as they are usually at a camp which provides a great backdrop for exciting escapades.
Another theme is the exploration of their individual growth influenced by each other. Nikki's wild nature might influence Max to be more carefree, while Max's more cynical side could make Nikki think more deeply about things. Fanfics often delve into how they impact each other's personal development while at camp.
One great 'camp camp nikki x max fanfiction' story is 'The Adventure Together'. It shows Nikki and Max going on a secret exploration in the woods near the camp. They face various challenges and in the process, their relationship deepens in a really interesting way.
You can try searching on fanfiction platforms like Archive of Our Own (AO3). It has a large collection of fanfics from various fandoms, including Camp Camp. Just use the search function and type in 'Camp Camp Nikki x Max' to see what's available.
I'm not sure who Nikki Yovino is just based on this title. She could be the author of the story, in which case she might be a writer or storyteller. She might be writing from her own experiences or from her imagination.
It's hard to say for sure. Some of the stories might be based on real events, but they could also be exaggerated or fictionalized for entertainment purposes.