Yes, there are quite a few. You can start by checking out some popular fanfiction websites like Archive of Our Own. Just search for 'oc son of greyjoy' and you'll likely find a variety of stories with different themes and plotlines.
One common theme is loyalty. Since the Greyjoys are known for their strong sense of loyalty to their family and the Iron Islands. Another theme could be the struggle for power. The son of Greyjoy might be vying for a position of power within the islands or against other houses in the 'Game of Thrones' world.
He could be a new character created by the fanfiction writer. Maybe he's a strong and ambitious son of Greyjoy, with a desire to prove himself in the cut - throat world of Westeros, much like the other Greyjoy characters we know from the original series.
He could play the role of a hero. In a fanfiction, he may be the one to save the Iron Islands from a great threat, like an impending invasion or a natural disaster. He uses his wits and courage, which might be different from the typical brute force associated with the Greyjoys. He could also be a diplomat, forging new alliances for the Iron Islands, like making a pact with the Lannisters to gain wealth and protection in exchange for naval support.
Power struggle is a very common theme. The Greyjoys are known for their thirst for power in the Iron Islands, and in fanfictions, oc characters often get involved in battles for supremacy within the family or against other houses.
Yara herself is a complex character. She's strong - willed, a leader, and has her own set of values. In OC fanfiction, we can see how different types of OCs interact with her. A timid OC might be inspired by her, or a power - hungry OC could clash with her. This creates a lot of potential for interesting storylines. Also, the power dynamics in the Iron Islands, with their focus on seafaring and raiding, provide a great backdrop for any story involving Yara and an OC.
Power dynamics is also a common theme. Theon is part of the Greyjoy family which has its own power struggles, and when the OC enters the picture, how they navigate these power dynamics together is often explored. Additionally, identity is a theme. Theon has had his identity questioned and the OC can either help him redefine it or struggle with his ever - changing sense of self.
I also like 'The Lost Greyjoy'. In this one, the oc Greyjoy is a forgotten member of the family who returns with a vengeance. The story is full of twists and turns as the character tries to reclaim their place among the Greyjoys, and it also has some great descriptions of the Iron Islands.
One great Yara Greyjoy OC fanfiction is 'The Sea Queen's Ally'. It features an original character who becomes a trusted companion to Yara. The story is full of adventure on the high seas, with battles and political intrigue.
Well, there's 'A New Dawn for Theon and OC'. It's set after Theon's many trials and the OC enters his life as a glimmer of hope. The story is really good at showing their emotional connection and growth. I also like 'Theon's Bond with the OC' which focuses on how their relationship forms against the backdrop of political intrigue in the Iron Islands. It has some great character interactions that make it stand out.