In this fanfiction, Dawn turning into a vampire could lead to a situation where she tries to find a cure. Along the way, she might meet other vampires who have different views on their existence. Some might want to help her find a cure, while others would try to stop her as they see her as a threat to their way of 'life'.
One possible plot could be Dawn's struggle to control her new vampire instincts while still maintaining her relationships with the Scooby Gang. She might have to hide her transformation from Buffy at first, leading to a lot of internal conflict.
Perhaps Dawn becomes a vampire and discovers she has unique powers compared to other vampires. This could draw the attention of both good and bad forces in the Buffy universe. She could then be caught in the middle, trying to figure out which side she truly belongs to.
The Scooby Gang would also be affected. Xander might be more hesitant and scared, while Willow could try to use magic to help Dawn. Giles would probably be the voice of reason, trying to figure out the best course of action. And Spike, being a vampire himself, could have a complex reaction. He might see Dawn as a new addition to the vampire world or feel some sort of loyalty to Buffy and try to help Dawn resist her new nature.
Well, in some 'Buffy turns into a vampire' fanfiction, there could be a plot where Buffy has to deal with the rejection of her friends at first. But then they realize that she's still Buffy deep down. Also, she could team up with some vampires who oppose the more evil ones, using her new vampire abilities for good in a way that no one expected.
There might be a fanfiction where Dawn travels back in time and meets a younger version of Buffy. This could lead to some really interesting interactions and changes in the timeline.
One common theme is the struggle between good and evil. Since it involves vampires, there's often a battle between the forces of darkness (the vampires) and the forces of good, with Dawn sometimes caught in the middle.
One common theme is identity. Since Dawn becomes a vampire, she has to re - evaluate who she is. Another theme is family. Buffy's reaction to Dawn's new state and how they interact as sisters in this new situation is often explored.
One common theme is identity. Dawn has to figure out who she is as a vampire, different from her human self. Another theme is family. Buffy and the rest of the gang have to deal with Dawn in this new state, which tests their family bonds.
Well, she might struggle with her newfound vampiric nature. Maybe she would try to resist the urge to feed on humans, like Angel did. She could also find herself at odds with Buffy, who would be torn between protecting her sister and fighting the vampire she has become.
In a 'Harry turns into a vampire' fanfiction, the story could start with Harry being cursed by a powerful and ancient spell that turns him into a vampire. His friends at Hogwarts are initially scared and unsure how to deal with him. However, Harry is determined to find a way to reverse the transformation. Along the way, he discovers that there are some positive aspects to being a vampire, such as heightened senses that help him in his detective - like investigations into the origin of the curse.
The fanfiction could go like this. Sonic is on a mission in a spooky, abandoned town. Unbeknownst to him, it's infested with vampires. One of them manages to turn him into a vampire. At first, Sonic is horrified. His appearance changes slightly, with paler fur and redder eyes. He has to learn to live with his new condition. His friends like Tails and Knuckles are confused and a bit scared. However, Sonic discovers that being a vampire gives him the ability to sense danger from afar. He then uses this to his advantage to protect the town and his friends from an even greater evil that's lurking in the shadows. Eventually, he might find a way to reverse the transformation and return to his normal self.
I think there are several such fanfictions out there. You might find one on popular fanfiction websites like Archive of Our Own or FanFiction.net. But specific titles could vary.