Some common themes are secrecy and discovery. The idea of Naruto and Sasuke having to be extremely careful not to be found out is a big part of it. There's also the theme of self - discovery. As they enter this relationship, they learn more about themselves and their emotions. Additionally, the theme of loyalty comes into play. They have to balance their loyalty to each other in the relationship with their loyalty to the village and their ninja duties.
One common theme is the secrecy itself. Writers often explore how Naruto and Sasuke have to hide their relationship from their friends like Sakura and Kakashi. Another theme is the internal struggle they face. They might struggle with their own feelings, especially considering their past as rivals. Also, there's the theme of acceptance. How they come to accept their feelings for each other and deal with the potential rejection from others in the ninja world.
Common themes include the challenges of keeping their relationship a secret. For example, they might have to meet in secluded places to avoid being caught. Another theme is the growth of their relationship. It starts from their initial hesitation and gradually develops into a deep love. And there's also the theme of the outside world's reaction. How would the village react if they found out? This creates a lot of drama and tension in the fanfiction.