Love and protection are very common. Itachi is often depicted as a very protective figure towards the reader. He will go to great lengths to keep the reader safe from harm, whether it's from his own clan's enemies or other threats in the Naruto universe.
One common theme is the struggle between loyalty and love. Itachi has his loyalty to his village and clan, and the male reader may have his own allegiances. Their relationship has to navigate through these complex loyalties. For example, in many fics, Itachi's actions for the sake of his village put a strain on his relationship with the male reader.
One common theme is unrequited love. Itachi may be pining for Sakura while she is oblivious or has feelings for someone else. Another theme could be sacrifice, where Itachi's feelings for Sakura lead him to make sacrifices he wouldn't otherwise make.
The theme of destiny is quite common. Itachi might believe that Naruto is part of some greater destiny, and his own actions are somehow intertwined with Naruto's. In these fanfictions, Itachi's obsession can be a driving force in fulfilling that shared destiny. Additionally, the theme of understanding is there. Itachi tries to understand Naruto's unique power and personality, and through this understanding, his obsession grows.
Friendship is a common theme. The reader character might form deep friendships with Itachi and Kisame, going on adventures together and relying on each other. Another theme could be mentorship, with Itachi or Kisame teaching the reader character new skills or knowledge about their world.
One common theme is sacrifice. Itachi often has to make difficult choices for the greater good, and this can impact his relationship with the reader. Another theme is the secrecy and hidden nature of their love, as Itachi's situation in the ninja world doesn't always allow for open relationships. Also, redemption can be a theme, as the reader may see the good in Itachi despite his past actions.
One great 'itachi x reader' fanfiction is 'A Meeting with Itachi' on FanFiction.net. It really delves into the deep connection between the reader and Itachi. The story has a really engaging plot where the reader character has a fateful encounter with Itachi and from there, a very intense relationship begins to develop. It's full of emotional moments and great character development.
A prevalent theme is redemption. Given Itachi's complex past, the fanfictions might explore how he tries to make up for his actions in the presence of the reader and Sasuke. Also, self - discovery can be a theme. The reader may be new to the Naruto world and through their interactions with Sasuke and Itachi, they learn more about themselves and their place in this fictional world. In some stories, there's also the theme of protecting one another, showing loyalty and trust among the three characters.
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.