One common theme is the struggle between love and power. Since Itachi is a vampire, he often has to balance his newfound power with his love for Sasuke. Another theme is the idea of forbidden love, as their relationship might be seen as taboo in the context of vampire and human (or in this case, another Uchiha).
Reconciliation is a big theme. Itachi and Sasuke's relationship is often at the center of this. Naruto can be the catalyst in these stories, helping them to reconcile their differences. There are also themes of sacrifice, as Itachi has already sacrificed a lot in the original story, and fanfictions may expand on this concept in relation to all three characters.
The theme of sacrifice also often appears. Itachi sacrificed a great deal for Sasuke and the village. Fanfics might expand on this, like showing how Sasuke comes to fully understand and appreciate Itachi's sacrifices, and how that understanding changes their relationship.
Another theme is redemption. Itachi, in particular, has a lot of room for redemption arcs in these fanfictions. His actions in the original series can be re - examined and re - shaped in the context of his relationship with Naruto and Sasuke. Also, friendship evolving into something deeper is a big theme. Naruto and Sasuke's friendship is a central part of the original Naruto story, and in these yaoi fanfictions, it can take on new dimensions when Itachi is added to the mix. They all support and challenge each other, which is a recurring idea in many such fanfictions.
A lot of these fanfictions have the theme of sacrifice. For example, Sasuke might have to sacrifice his vampire nature or Sakura might sacrifice her normal life to be with the other. Also, there's often the theme of redemption. If Sasuke has done bad things as a vampire, he may seek redemption through Sakura. And of course, there's the overarching theme of love and how it can overcome differences and obstacles, like the fact that one is a vampire and the other is human.
One common theme could be the complex relationship between Itachi and Sasuke. Their bond, which is filled with love, hatred, and a lot of unsaid emotions in the original series, is often explored more deeply in fanfics. Another theme might be redemption, as Itachi's actions towards Sasuke in the main story can be seen in different lights in fanfiction.
A common theme is protection. Itachi is often depicted as protecting baby Sasuke from various threats. Another theme is brotherly love. It shows their bond even when Sasuke is just a baby. Growth is also a theme, as we can see how Sasuke might grow up under Itachi's influence in the fanfiction.
One common theme is redemption. Sasuke often sees Itachi in a new light and this helps him find a path towards redemption. He realizes that Itachi was not the monster he once thought and his love for Itachi becomes a part of his journey to make amends for his past actions.
One common theme is revenge. Sasuke's thirst for revenge against Itachi is often explored in great detail. Also, friendship, especially Naruto's friendship with Sasuke, is a big theme. Naruto's attempts to bring Sasuke back from the path of vengeance. Another theme is sacrifice, as Itachi's self - sacrificing actions for the greater good are often a central part of the stories.
One common theme is brotherly love. Itachi's love for Sasuke despite the hardships they face is often explored. For example, in many fanfictions, Itachi sacrifices a lot to protect Sasuke.
One common theme is the struggle against family and clan expectations. In the Naruto universe, the Uchiha clan has a strict code. Sasuke being in love with Itachi goes against the normal family dynamic. Another theme is self - discovery. Sasuke has to come to terms with his feelings which are not only unorthodox but also might make him question his identity.