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.
Well, an OC (Original Character) son of Bolton could be a really interesting addition to a fanfiction. He might be a cruel and calculating character, given the Bolton family's reputation in 'Game of Thrones'. He could be vying for power in the North, perhaps trying to outwit the Starks or other northern houses. Maybe he has some unique skills, like being an expert tracker or a master of psychological warfare.
Theon could be a great character to pair with Yara. Their complex relationship as siblings could be explored further. Maybe in the fanfiction, they work together to redeem the Ironborn's reputation after all the chaos caused by Euron.
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.
One possibility could be that the oc, being the son of Drogo, has a claim to the Dothraki leadership. He could strive to unite the Dothraki clans in a different way than Daenerys did. Maybe he focuses on forging alliances with the other kingdoms based on mutual trade and protection rather than conquest.
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.
I think it could be the blacksmith OC who has a strong moral code. For instance, an OC who refuses to make weapons for evil lords or sells his work only to those who he believes will use it for good. This type of character adds depth to the fanfiction and can be very appealing to readers who like complex and morally upright characters.
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.
One interesting fanfiction could be about Yara leading the Ironborn in a new conquest. Maybe she discovers a hidden island full of treasures and has to battle both external enemies and deal with internal power struggles among her own people.