A great fanfiction could be centered around Dawn's struggle to fit in at school while also dealing with her supernatural knowledge. She tries to make normal friends but has to keep her true identity a secret, which creates a lot of internal and external conflicts.
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 interesting fanfiction could be about Spike's redemption arc in an alternate universe. Maybe he meets Buffy much earlier and their relationship develops in a completely different way, with him being more of a reluctant hero from the start. Another could be a time - travel story where Buffy and Spike are sent back to a crucial moment in the show's history and have to change things without messing up the timeline too much. And there are also those that focus on their emotional connection, like a story where Spike has to deal with his love for Buffy while she's in a coma.
One interesting story could be where Buffy meets the Cullens from Twilight. Maybe she initially suspects them of being dark vampires but then realizes they have a different code. Another could be a crossover where the Scooby Gang has to deal with the Volturi's power plays in Sunnydale. There are also fics where Buffy and Edward team up to fight a common vampire foe that is stronger than both their usual adversaries.
Some Xander fanfiction focuses on his love life in a more unique way. He could fall for a new character, a half - vampire half - human girl perhaps. Their relationship would be full of drama as they struggle with their different natures and the Scooby Gang's reactions.
One common theme is protection. Spike often ends up protecting Dawn from various threats, whether it be vampires or other supernatural beings. It shows his growth from a more self - centered character to someone who cares about Dawn's well - being.
One common theme is protection. Since Spike is a powerful vampire, many fanfics have him protecting Dawn from various threats in Sunnydale. Another theme is friendship. They often form a unique bond that is different from their relationships with other characters in the show.
I'm not sure about the absolute best, but some popular ones might be those who have a deep understanding of the Buffy universe. They know all the characters well, especially Dawn, and can write her in - character. For example, an author who has been following the show since it started and has a passion for Dawn's character arc.
One idea could be a crossover where Naruto's world is invaded by vampires. Buffy could travel to the Naruto universe to help fight them using her slaying skills and knowledge, while Naruto and his friends learn about the existence of vampires.
One idea could be an OC who is a witch from a long - lost coven that has a unique power related to time manipulation. This OC could accidentally get involved in Buffy's battles when trying to correct a time - related mishap in the supernatural world. Another idea is an OC who is a half - vampire, half - human hybrid, struggling to find their place between the two worlds. They could initially be seen as an enemy by Buffy but later become an ally.
One great fanfiction could be 'Dawn's Discovery'. In it, Dawn finds herself in a dangerous situation and Spike is the only one who can protect her. It delves into their unique relationship, with Dawn seeing Spike in a new light and Spike realizing his role as her protector.
One great place to start looking for Buffy the Vampire Slayer Spike and Dawn fanfiction is Archive of Our Own (AO3). There are numerous stories there. For example, 'The Unlikely Bond' is a fanfic that delves into how Spike and Dawn form an unexpected friendship after a series of supernatural events in Sunnydale. It's really interesting as it shows their characters evolving in new ways outside of the main show plot.