Another theme is redemption. Sometimes the oc tries to redeem Voldemort or is on a journey of self - redemption while being associated with him. They might see some good in him that no one else does and strive to bring it out. It adds a lot of depth to the story. And also, the theme of survival is quite prevalent. The oc has to survive in the dangerous world dominated by Voldemort and his Death Eaters, constantly facing threats and having to outwit their enemies.
Power is a common theme. The oc often has to deal with Voldemort's thirst for power and either resist it or be drawn into it. For example, in many fics, the oc discovers a new form of magic that Voldemort wants to use for his own evil purposes.
Love or obsession is also a frequent theme. Sometimes, there's an unexpected love story between them, which is quite a contrast to their original characterizations. Other times, it's more of an obsession on Voldemort's part towards Bella. This can lead to complex relationships and storylines that keep readers hooked as they try to understand the nature of this unusual connection.
One common theme is loyalty. Bellatrix is extremely loyal to Voldemort in the original series, and this is often explored more deeply in fanfiction. For example, stories might show her unwavering commitment to him even in the face of great danger.
A prevalent theme is the dark nature of their relationship. It's often depicted as being based on a mutual love for the dark arts and a desire for domination. In some fanfictions, there's also the theme of obsession. Bellatrix's obsession with Voldemort is a central part, like in the fanfiction 'The Darkest Devotion' where her every action is centered around pleasing and serving Voldemort. And of course, the theme of fear also plays a role, as many characters in the wizarding world fear their combined might.
Common themes include the exploration of dark magic. If Harry is Voldemort, he would be more involved with dark magic, so the fanfictions often show his journey into that world. Also, the theme of redemption might be present. Even though he's in the form of Voldemort, he might try to atone for Voldemort's past deeds. And there's always the theme of how the wizarding world reacts to this strange transformation of Harry.
The theme of the dark side of magic can also be prevalent. Since both are dark wizards, fanfictions may explore their use of dark magic together. It could include their experiments with curses, or how they plan to use dark magic to achieve their goals, like taking over the wizarding world. Their relationship might be intertwined with their shared love for the most dangerous and forbidden forms of magic.
It might be considered somewhat common. Since Voldemort is such an iconic and complex villain in the Harry Potter series, adding an oc to his fanfiction gives writers the chance to explore different relationships and storylines. For example, an oc could be a love interest for one of Voldemort's followers, or a secret weapon against him. However, it's not the most dominant trope, but still quite popular among those who write fanfiction in this genre.
One common theme is the struggle of Hermione against Voldemort's power. Even when she is in a position of submission, she often tries to resist in some way. Another theme could be the exploration of the dark side of the wizarding world. It shows what could happen if a strong character like Hermione is forced into the service of evil. Also, the idea of redemption or escape is often present. Fans might write about Hermione finding a way to break free from Voldemort's control and turn the tables on him.
One common theme is the power of knowledge. Hermione is known for her studious nature, and in these fanfics, her knowledge often becomes the key to defeating Voldemort. For example, she might use some obscure magical theory or historical fact to turn the tables on him.
One common theme could be redemption. Maybe the story shows voldemort changing through his relationship with harry. Another theme might be the power dynamics, as both are very powerful in different ways.
Power is a common theme. Since Voldemort is a very powerful dark wizard and Bella is his devoted follower, their relationship in fanfiction often revolves around power sharing or Bella gaining power through her connection to Voldemort.