In Sasuke x Orochimaru yaoi fanfic, a prevalent theme is the mentor - student relationship gone awry. Orochimaru was initially Sasuke's mentor in a way, but with a yaoi twist, it becomes a much more complex and often romantic or sexually charged relationship. Another common theme is the struggle between light and dark. Sasuke has his own internal battle, and Orochimaru represents a darker side. Their relationship in these fanfics can be a way to explore how these two sides interact and potentially merge or conflict.
Common themes often include the idea of forbidden love. In the Naruto universe, the relationship between Sasuke and Orochimaru is complex and not exactly a typical positive one. So in yaoi fanfics, the forbidden nature of their relationship can add an element of drama and intrigue. Also, there might be themes related to self - discovery. As Sasuke and Orochimaru interact, they could learn more about themselves and their desires.