The main protagonist from the original 'the black arrow' is likely to be very popular in the fanfiction as well. Their heroic deeds and journey are often the focus.
One interesting story could be about the adventures of the main character in a new and dangerous land. They might face various challenges and make new allies.
Another theme is the exploration of their individual powers and how they complement each other. The Arrow's archery skills combined with the Black Canary's sonic scream make for some exciting battle scenarios. A lot of fanfictions play around with how they can use these abilities in different situations to defeat villains.
There might be a story where the Black Arrow teams up with an unlikely ally. For example, a young thief who has a heart of gold. Together, they take on a powerful and corrupt lord in the region.
The Green Arrow and Black Canary's romance in fanfiction is often exciting. Fanfic writers can explore their relationship in different ways. Some might focus on their initial attraction, like how their first encounters in the fictional world of the story could be filled with tension and a spark of something more. They could be in the middle of a dangerous mission and realize they have feelings for each other.
There's also 'Black Canary and Green Arrow: Partners in Peril'. This fanfiction takes them on an adventure outside of Star City. It has a great plot that includes some classic villains. The way it portrays their teamwork and the growing affection between them is really well - done.
Well, a very popular theme is their partnership. Fanfictions often show how they combine their skills, with Green Arrow's archery and Black Canary's sonic scream, to take on bad guys. Family also comes up sometimes. Maybe Black Canary's family history or Green Arrow's family legacy and how it affects their relationship and actions. And of course, there are the stories that focus on their adventures in different parts of the DC world, like in Gotham or Metropolis.
I'm not entirely sure if there is a specific amount of Green Arrow and Black Canary pregnant fanfiction. It really depends on how creative the fanfiction writers in that fandom are. Some writers might be interested in exploring this aspect of their relationship, while others may focus on different storylines. You could try looking on platforms where DC Comics fanfiction is shared.
Character development is key. See if the fanfiction delves deeper into the Black Arrow's character, his backstory, and how he evolves. Also, a good plot that fits within the existing Arrowverse lore is great.