One challenge is merging the two very different universes. NCIS is more about traditional law enforcement and military investigations, while Watch Dogs is centered around hacking and a cyberpunk - like urban environment. Another challenge is keeping the characters' personalities true to their original portrayals. For example, Gibbs from NCIS has a very distinct way of leading his team, and it can be hard to make that work when combined with the more tech - savvy and edgy characters from Watch Dogs. Also, the technology in Watch Dogs can be quite complex, and explaining it in a way that fits into the NCIS world without making it seem out of place is difficult.
One common theme is friendship evolving into something more. Abby's friendly nature makes it easy to build a connection with other female characters in fanfiction, and often that connection deepens over time. Another theme is the contrast between Abby's goth - like appearance and her sweet personality with the other female character's own distinct traits.
One common theme is romance. Writers often explore the relationship between Delilah and the OC, showing how they fall in love, overcome obstacles, etc. Another theme could be mystery, as NCIS is a crime - solving show. The OC might get involved in a case and work alongside Delilah to solve it.
There's also 'Tony and Kate: A Different Perspective'. This fanfic takes a unique approach, showing their relationship from the eyes of other NCIS team members. It gives an interesting view on how their dynamic is perceived within the team and how it affects the overall work environment.
Many NCIS Gibbs x OC fanfictions focus on the OC's backstory and how it intersects with Gibbs' life. For example, if the OC has a military background like Gibbs, it can create a connection between them. Also, there are themes of redemption. If the OC has made mistakes in the past, the story might be about them finding a new purpose and a new family within the NCIS team led by Gibbs.
Maybe there's a hidden Templar plot that has ties to a military case the NCIS is investigating. An Assassin discovers this connection and has to work with the NCIS agents, who are initially skeptical of this person with such strange abilities and knowledge. They gradually learn to trust each other as they uncover the Templar conspiracy together.
In Naruto x NCIS fanfiction, a cool concept could be a crossover mission. Imagine the NCIS team having to deal with a threat that has ties to the ninja world. The NCIS agents' forensic skills combined with the ninjas' combat and stealth abilities would make for an exciting story. For instance, Zoro from NCIS could learn some basic ninja moves from Naruto to enhance his own combat skills in a particular case.
One great 'NCIS LA and NCIS Crossover Fanfiction' is 'The Joint Operation'. It combines the unique characters from both shows really well. The plot usually involves a case that requires the expertise of both teams. It shows how the agents from NCIS and NCIS LA interact, like how Gibbs' no - nonsense approach clashes and also gels with Hetty's more mysterious style of leadership.
It could be really exciting. Imagine the characters from Hunter x Hunter with their unique nen abilities in the world of NCIS investigations. Gon could use his enhanced senses to help Gibbs' team track down clues. Killua's assassin skills might come in handy during dangerous undercover operations. And the NCIS agents would be both baffled and intrigued by these strange new allies.
Fanfiction.net is a great place to start. It has a large collection of NCIS fanfics, including many centered around Tony and Kate. You can search by the show name and then filter for the specific pairing.