One common theme is adventure. The reader often goes on exciting quests or missions with Azriel. For example, they might explore a mysterious new land in Prythian together.
You can try looking on Archive of Our Own (AO3). It has a large collection of fanfics, and there are likely many azriel x reader ones there. Just use the search function and type in 'azriel x reader' to filter the results.
There is a popular 'azriel x reader fanfiction' titled 'In Azriel's Arms'. It's a must - read because it shows a very unique side of the relationship. It has a great plot that keeps you hooked from the start, with the reader character having some really interesting interactions with Azriel.
Tumblr can be a good source too. There are many blogs dedicated to fanfiction, and you might be able to find some amazing 'azriel x reader fanfiction' by searching relevant tags or following the right blogs.
You can try searching on popular fanfiction websites like Archive of Our Own (AO3). There are often a large number of fanfics for various pairings, and it's likely you'll find some great 'elain x azriel' ones there.
The theme of self - discovery also frequently appears. As their relationship develops, both Elain and Azriel discover new sides of themselves. For example, Elain might find a new strength within her because of Azriel's belief in her, and Azriel might open up more about his past traumas due to Elain's kindness.
One of the common themes is the exploration of their individual powers and how they complement each other. Azriel with his shadows and Elain with her seer abilities. Fanfics might show how they use their powers together or how their powers influence their relationship. Also, redemption is sometimes a theme. Maybe Azriel has some past mistakes he wants to make up for in relation to Elain, or Elain has to redeem herself in Azriel's eyes. And of course, the theme of self - discovery. As they get closer, they learn more about themselves.
One common theme is redemption. Often, either Azriel or Eris is portrayed as seeking redemption in some way, whether it's for past actions or for their family's reputation. Another theme is rivalry - turned - friendship. Their initial animosity towards each other slowly morphs into a form of respect and friendship in many fanfics.
Love and longing are very common. Since their relationship in the original context has a certain allure, fanfictions often explore the deep, unspoken feelings they might have for each other.