One of the main themes is family. Despite the complex relationship they have in the original story, in fanfiction with baby Sasuke and Itachi, it focuses on the positive family aspect. Loyalty is another theme. Itachi's loyalty to his little brother and Sasuke's budding loyalty towards Itachi as a baby are often explored. Additionally, the theme of mentorship comes up, with Itachi being a sort of mentor to baby Sasuke in the fanfiction world. It's about Itachi teaching Sasuke about the ninja world and values.
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.
Love and family are also very common themes. Itachi may have been a cold - blooded ninja before, but as a baby daddy, he discovers the warmth of love and the importance of family. There's also the theme of secrecy. Given his situation, he has to keep the existence of his child a secret from many people, which adds a lot of tension to the story.
One common theme is redemption. For example, Sasuke often has a journey of redeeming himself after his dark turn. Another theme is friendship, like how Naruto's unwavering friendship for Sasuke is a central part. Also, the idea of sacrifice, as seen with Itachi's great sacrifice for the village and his brother.
One common theme is redemption. For example, Itachi's actions are often explored in a way that he tries to atone for his past deeds. Naruto usually helps in this process as he believes in the good in people.
One common theme could be the exploration of Sasuke's emotional turmoil. Since Itachi is abusing him in this fanfiction, Sasuke might be shown as confused, angry, and deeply hurt. Another theme could be the power dynamic between them. Itachi being the abuser might have a significant amount of power over Sasuke, which could lead to themes of helplessness on Sasuke's part. Also, themes of revenge might be present. Sasuke might be constantly thinking about getting back at Itachi for the abuse, which could drive the plot forward in the fanfiction.
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).
One possible fanfiction could be about Sasuke finding a baby during his travels. The baby, having an unexplained connection to Itachi, starts to influence Sasuke's view of his brother. Sasuke might see the innocence in the baby and be reminded of the good in Itachi that he once overlooked.