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.
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 be a rebel. Tired of the Bolton family's traditional ways, he might try to change the family's reputation. He could be a force for good in the North, protecting the smallfolk from the usual Bolton brutality.
The OC Greenseer could act as a guide. They might use their visions to lead characters to hidden treasures or safe havens. For instance, they could show a group of refugees the way to a secret valley where they can survive the winter and the war.
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.
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.
Margaery can also be a symbol of hope or change in fanfictions with a male OC. If the male OC is disillusioned with the current state of Westeros, Margaery could represent a new way forward. Her charm and intelligence can inspire the male OC to support her in her plans to reform the kingdom. Their relationship then becomes a driving force for the plot, as they strive to make Westeros a better place while also dealing with their own personal feelings for each other.
Petyr Baelish often plays a devious role in OC fanfiction. He might be the mastermind behind many plots. For example, he could be using an OC to gain more power in King's Landing.
He could also play the role of a healer. In a world full of wars and diseases, a male OC with exceptional healing skills would be very valuable. He could be in a small town when a plague breaks out. He uses his knowledge of herbs and ancient healing techniques to save as many people as he can. This would make him a hero in the eyes of the common people, and perhaps catch the attention of a powerful noble who wants to use his skills for their own purposes.
A female Stark OC could play the role of a peacemaker. For instance, if there are disputes between different Stark siblings or between the Starks and other houses. She could use her diplomatic skills, which she might have learned from observing her father. Her calming presence and ability to see different perspectives would help in resolving conflicts.
Perhaps the OC son has a special ability or gift that Jon Arryn was trying to protect him from being exploited for. After Jon Arryn's death, the son has to learn to control this ability while also dealing with the power struggles in King's Landing. He could be a key figure in the fight against the White Walkers, using his unique skills to help the living, all while trying to uphold his father's legacy.