In some 'dark angel buffy crossover fanfiction', the characters' backstories are explored in relation to each other. Maybe Buffy discovers that there are some similarities between her calling as a slayer and Max's situation as a genetically enhanced being. They could bond over their sense of being different from the normal humans around them and their responsibility to protect those who can't protect themselves. This type of fanfiction often delves deep into the emotional and psychological aspects of the characters, making it a more complex and interesting read.
Fanfiction.net is also a good place to search. There are many different categories and tags, so you can specifically look for crossovers between 'Dark Angel' and 'Buffy'. Just be prepared to sift through a lot of stories to find the ones that interest you the most.
One idea could be that the vampires in Buffy's world somehow cross over to the Dark Angel universe and the transgenic characters have to deal with them. They might initially mistake vampires for some new kind of transgenic experiment gone wrong. Another idea is that Buffy herself travels to the Dark Angel world and teams up with Max to fight against a common enemy that is threatening both of their worlds, like a powerful demon that has found a way to use transgenic technology for evil purposes.
In my opinion, Faith from Buffy and Alec from Dark Angel would be great to focus on. Faith has her own troubled past and her unique slayer abilities. Alec, on the other hand, is a transgenic with a bit of a roguish charm. The two of them could have a really interesting dynamic. Maybe they start off as rivals, not trusting each other, but as they face a common enemy, they start to understand and respect each other. And of course, Buffy and Max are also must - haves. They are the main characters of their respective shows and their leadership skills and different outlooks on life would make for a great story.
A common theme is the rekindling of their relationship. Whether it's a romantic or a platonic bond, it often focuses on how they reconnect. Another theme is the fight against a greater evil. Since both are from the Buffyverse which is full of demons and dark forces, this is a natural theme.
One great 'angel and buffy crossover fanfiction' is 'Crossed Paths'. It beautifully weaves their two worlds together, exploring their complex relationship in a new and exciting way. Another one could be 'Reunion' which focuses on how they handle a new threat together after being apart for a while.
Love and sacrifice are common themes. Their relationship has always been about love in different forms and often one has to sacrifice for the other. So in crossovers, this is often explored further.
One popular one could be 'Soulmates Across Dimensions'. It beautifully weaves the two universes together, exploring how Buffy and Angel's relationship might develop further in new and unexpected ways. It has some great action scenes and emotional moments.
One interesting Buffy Angel crossover fanfiction could be a story where Buffy and Angel have to team up to fight a new, more powerful vampire threat that is immune to their usual methods. This forces them to rely on each other in new ways and re - explore their relationship.
There's also 'Crossroads'. This fanfiction delves deep into the emotions of both Angel and Buffy. It explores how their past experiences shape their actions when they cross paths again. The writing is engaging and it really captures the essence of the two shows.