One common theme is the merging of their different backgrounds. Oliver has his own set of values from his upbringing in Star City, while Nyssa comes from the League of Assassins. Their marriage often involves them finding a common ground between these two very different worlds.
One popular 'Oliver and Nyssa married' fanfiction is 'A New Beginning'. It shows their life after getting married, dealing with family and the challenges of protecting the city together. It has great character development and an interesting plot.
One common theme is redemption. Nyssa has a complex past, and often in fanfiction, she is on a path of redemption, with Oliver being a part of that journey. For example, in many stories, Oliver helps her come to terms with her actions in the League of Assassins.
Love and sacrifice is also a big theme. Their relationship is complex, and often in fanfictions, they have to make sacrifices for each other or for the greater good. This can range from giving up their own desires to risking their lives. It adds a lot of depth to their relationship.
Thea Queen would be an interesting character to include. As Oliver's sister, she could have a unique perspective on their marriage and might be involved in family - related subplots. Also, Malcolm Merlyn could be a great antagonist in the fanfiction. His complex relationship with Oliver and his own motives could add a lot of drama to the story of Oliver and Laurel's married life.
One possible plot could be Oliver and Laurel navigating the challenges of being superheroes while married. They might have to balance their vigilante duties with their relationship, like dealing with secrets and the danger it poses to their family. Another could be them starting a family and how they raise their children in a world full of villains and chaos.
There's 'Married Bliss in Star City'. This fanfic focuses on the more domestic side of their marriage. It has cute moments like them cooking together, having movie nights, and also how they handle Oliver's vigilante duties while maintaining a loving relationship. It really gives a warm and fuzzy feeling about their married life.
One great Oliver and Nyssa fanfiction is 'A New Alliance'. It shows their relationship evolving in a really interesting way as they team up against a common enemy. The story has great character development and some really exciting action scenes.
You can start by searching on fanfiction platforms like Archive of Our Own (AO3). Just type in 'Arrow Oliver and Felicity married' in the search bar, and it will bring up a list of relevant fanfictions. AO3 has a great tagging system which helps in filtering out the ones you might be interested in.