Another theme could be the challenges they face together. Given their roles in the Naruto universe, they might encounter various threats or obstacles that they have to overcome as a team, which can strengthen their bond in the story.
The theme of redemption also pops up often. Since Itachi has a complex and somewhat dark past, the OC might be a factor in his journey towards redemption. And for Kakashi, the OC could be a new chapter in his life, helping him move on from past traumas or regrets. This makes for a very interesting dynamic in these fanfictions.
The theme of sacrifice is also prevalent. Given their complex situations, they may be required to sacrifice things for each other or for the greater good. This could be sacrificing their own safety, their reputations, or their relationships with others in the fan - created stories.
The theme of redemption can also be found. Maybe the female Itachi has some past mistakes or a dark side, and Naruto's influence helps her to find a path of redemption. Also, friendship and loyalty often play a role. As they face challenges together, they build a strong bond of loyalty and friendship, which is often tested in the fanfiction stories.
One common theme is mentorship. Even though it's a different dynamic with female Kakashi, Naruto still often looks up to her for guidance, just like in the original series. Another theme is the exploration of gender roles. Since Kakashi is now female, it can lead to interesting takes on how traditional ninja gender roles are either subverted or adhered to. For example, how she may lead Team 7 differently from the male Kakashi.
One common theme is the clash of their personalities. Itachi is calm and calculating, while Hidan is wild and impulsive. Fanfictions often explore how these two contrasting personalities interact. Another theme could be the exploration of their different beliefs. Itachi has his own complex moral code, and Hidan has his extreme religious views regarding Jashin.
One common theme is the clash of different worlds. Since Kagome is from Inuyasha's world and Itachi from Naruto's, there's often exploration of how their two very different universes interact. For example, different types of magic and combat styles.
Another theme is sacrifice. Given their fates in the original story, fanfictions often play around with the idea of how much they are willing to sacrifice for each other and for the greater good. It could be sacrificing their own lives or their own happiness for the other.
Power dynamics are also a frequent theme. Female Itachi and female Kisame are both strong characters in the Naruto universe. Fanfictions might explore how their powers interact with each other, and how they compare to other characters. Maybe they team up to take on a powerful enemy, or they have a power struggle within their relationship.
One common theme is mentorship. Kakashi is Naruto's teacher, and many fanfictions explore how this relationship develops over time. Another theme is friendship. As they spend more time together, their bond of friendship often becomes a central focus. Also, the theme of growth is prevalent. Naruto grows as a ninja and as a person with Kakashi's guidance.
The theme of mentorship or friendship - turned - love is also seen. Maybe Kakashi starts as a mentor to Kushina, or they begin as friends and then feelings develop over time. Another aspect could be the exploration of their pasts. Both characters have had difficult experiences in their lives. Fanfictions might explore how these pasts shape their relationship, like how Kakashi's experiences with his team and Sensei could influence his relationship with Kushina, and how Kushina's upbringing as a Jinchuriki affects her feelings towards Kakashi.