A really unexpected plot twist could be that the power of being a vampire lord is not what it seems. Instead of giving Harry strength, it's slowly draining his life force. And the only way to reverse it is to find a rare magical artifact that is protected by an old and powerful wizard. This would send Harry on a whole new adventure and change the direction of the story completely.
One possible plot twist could be that Harry discovers he's not actually a vampire lord in the traditional sense, but a new kind of hybrid created by an ancient magic. This would completely change his understanding of himself and his place in the vampire and wizarding worlds.
A great plot twist could be that the one who turned Naruto into a vampire lord was actually a long - lost relative who had an ulterior motive. For example, they wanted Naruto to help them take over the ninja world using his popularity and new vampiric powers.
One possible plot twist could be that the succubus is actually an ally sent by someone to test the Lightning Lord. Another could be that the succubus has a hidden power that can nullify the Lightning Lord's magic. Maybe she has a magical amulet that was not known before.
Another plot twist could be that Naruto's own chakra has an unexpected effect on the vampire. Perhaps it changes the vampire in some way, either making them more powerful or causing some sort of internal struggle within them. This would then have a big impact on their relationship as they both have to figure out how to deal with this new situation.
A possible plot twist could be that the cat - vampire discovers it can reverse the transformation. Maybe by finding a magical herb or performing a special ritual. Another twist could be that the cat - vampire is actually the key to saving the entire Warriors cat clans from a greater evil. Despite being feared at first, it turns out to be a hero. Or perhaps the cat - vampire is not the only one, and there are other hidden vampire cats in the clans that come forward to help or oppose it.
A possible plot twist could be that Sasuke's vampire condition was actually a curse placed on him by an old enemy of the Uchiha clan. This would add a whole new layer of mystery and revenge to the story. Another twist could be that Naruto discovers he has some sort of power that can either nullify or enhance Sasuke's vampire abilities. It would put their relationship in a new light as Naruto has to decide what to do with this newfound knowledge.
Well, a great plot twist could be that Percy is turned into a vampire but he was actually part of an ancient prophecy in the vampire world. As he struggles to adapt to his new life, he finds out that there are vampire hunters who are after him not just because he's a vampire, but because they believe he will bring about a great change in the vampire - human balance. Also, his transformation could be different from other vampires. Instead of craving blood right away, he has a strange attraction to something else, like the essence of magic, which is very un - vampire - like and causes confusion among the vampire clans.
The 'Harry is a Vampire Lord OC fanfiction' could be really interesting. Usually, it will involve a lot of world - building. Since Harry is a vampire lord, there will be a whole new set of rules for the magical world he inhabits. Maybe the wizarding society now has to co - exist with vampires in a different way. The OC characters can bring in fresh plotlines. For example, an OC could be a vampire hunter who initially wants to kill Harry but then realizes he's different from other vampires. It's all about exploring new relationships and power dynamics.
Well, it could be that Stiles' secret vampire fanfiction is actually a premonition. He starts writing about a particular vampire who then shows up in real life. But this vampire is different from the typical ones in the stories. Instead of being evil, it's trying to find a way to co - exist with humans. Stiles then has to use his knowledge from the fanfiction to help this vampire, all while still keeping his vampire - loving side a secret from his friends.
A possible plot twist could be that the OC is actually related to one of Ryuga's old enemies. This revelation would create a huge conflict in their relationship. Ryuga would have to decide whether to trust the OC or not. Another twist could be that the OC has a hidden power that is somehow connected to the dark power Ryuga has, but in a way that could either destroy or save him.
A third plot twist could involve a character we least expect coming to Harry's rescue. Perhaps a Slytherin student who has been secretly against Voldemort all along. This student could have some inside knowledge about Voldemort's lair and manages to free Harry, leading to a change in the dynamic between the houses at Hogwarts.