One common theme is the forbidden love aspect. Since Sasuke and Hinata are from different clans in the Naruto universe, adding the vampire element makes it even more complex and forbidden. Another theme could be the power struggle. If Sasuke is a vampire, he might have powers that are difficult to control, and Hinata could be the one to help him. Or vice versa.
Well, a frequent theme is the transformation. If Sasuke or Hinata (or both) are vampires, their transformation into vampires and how they adapt to their new nature is often explored. Also, the theme of loyalty comes up. How loyal are they to each other in this new and dangerous situation? And there's also the theme of secrecy. Vampires usually have to keep their identity a secret, and this adds an extra layer of drama to their relationship in the fanfiction.
Common themes include the exploration of the vampire world. How does it function? What are the rules? And how do Sasuke and Hinata fit into it? Another theme is the protection of loved ones. Sasuke might want to protect Hinata from the dangers of the vampire world, or Hinata could be the one protecting Sasuke from other threats. And of course, there's the theme of sacrifice. They might have to sacrifice something in order to be together in this vampire - themed scenario.
The theme of transformation is also quite common. Sasuke's vampire state may lead to Hinata changing in some ways, perhaps becoming more confident or learning to fight better to be at his side. And vice versa, Sasuke might transform his view of the world and his place in it because of Hinata. There's also the mystery theme, as vampire lore usually brings an air of mystery to the story.
One common theme is the forbidden love aspect. Since Sasuke has his own dark and brooding nature as a vampire and Hinata is often portrayed as a gentle soul, their relationship is seen as something that goes against the norm in the Naruto universe.
One common theme is redemption. Sasuke often needs to find his way back to the good side, and Hinata can be a part of that journey, like in many stories where her kindness helps him. Another theme is growth. Both characters grow as individuals and in their relationship. For example, Hinata might become more confident in the presence of Sasuke, and Sasuke might learn to open up more.
One common theme is the struggle between Hinata's human side and her new vampire nature. She often has to deal with new instincts and powers that conflict with her gentle and shy human personality.
One common theme is the struggle between Sasuke's vampire nature and his humanity. He often has to deal with his bloodlust while still trying to hold on to his old self. Another theme is the isolation that comes with being a vampire. Sasuke is usually depicted as being alone or having a hard time fitting in with normal humans or even other vampires.
Often, there's the theme of the unexpected. Since Sasuke was mainly associated with Sakura in the original story, the idea of him falling for Hinata is unexpected. Also, the theme of self - discovery is present. As Sasuke falls for Hinata, he discovers new aspects of himself and his ability to love and be loved. There may also be themes related to family acceptance, as they come from different clans.
A common theme is cultural differences due to their clan backgrounds. Also, there's often the theme of love against all odds. Since in the original series they don't end up together, fanfiction writers like to show how they can overcome the odds and build a loving marriage. There can also be themes related to protecting their new family and dealing with threats from the outside world.
One common theme is the adjustment period. They come from different backgrounds, so stories often focus on how they adapt to living together. Another theme could be family acceptance, especially considering Sasuke's complex past.
One common theme is the exploration of a relationship that was not in the original Naruto story. It often involves Sasuke breaking away from his usual aloofness towards Hinata. Another theme could be Hinata's growth in confidence as she is loved by Sasuke.
Love against all odds is also a big theme. In these fanfictions, Naruto and Hinata often have to face opposition from the village or other vampires because of their relationship. Their love has to overcome these obstacles.