Suppose Jon Arryn's son forms an alliance with the Iron Islands in fanfiction. This would be a very different scenario from the original plot. With the Iron Islands' naval power and his own claim to power in the mainland, they could create a new power bloc. This could disrupt the balance of power between the other houses and change the way wars are fought and alliances are made in Westeros.
He could impact the story by influencing the Vale. Since Jon Arryn was an important figure in the Vale, his son would have had a certain amount of power and respect there. He might have been able to raise an army from the Vale earlier than what happened in the original story, and this army could have been a deciding factor in battles, like the ones during the War of the Five Kings.
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.
The OC son could start off as a naive and sheltered young man, but after Jon Arryn's death, he is forced to grow up quickly. He becomes more cynical and distrustful of those around him, especially the nobles in King's Landing.
One interesting fanfiction could be about Jon Arryn's son surviving in secret and emerging to claim his father's legacy. He might have been hidden away by a loyal servant and grows up in exile, learning the ways of the world far from the politics of King's Landing. When he returns, he causes a stir as he tries to uncover the truth about his father's death.
In this fanfic, the plot might be centered on a power struggle. Jon Arryn, being a powerful man, and Brightflame's wife, who might have her own resources or influence, could be caught in a battle for control. They could start off as allies, but as the story progresses, their own ambitions might drive them apart. Their relationship then becomes a complex dance of power, loyalty, and betrayal, with the fate of the Seven Kingdoms hanging in the balance.
The plot could involve a time - travel or alternate universe scenario. Maybe Blackfyre is brought to the present time in the Game of Thrones story (or an alternate version of it), and Jon Arryn marries her out of love. Their relationship then has to face the challenges of the existing power structures, the plots of other houses, and the secrets that Blackfyre might carry from her own past. This could lead to a whole new set of alliances and enmities within the Seven Kingdoms.
Well, if Jon Arryn married a Targaryen in a fanfic, it could completely change the power dynamics in Westeros. For one, it might strengthen the position of House Arryn, as the Targaryens have a powerful lineage. This union could potentially lead to different alliances. Maybe they would have had children who could have been claimants to the Iron Throne, adding more chaos to the already complex web of power struggles. Also, it could change the relationship between the Vale and other regions. The Vale might become more involved in Targaryen - related matters, like the fight for the throne or the conflict with the other Great Houses.
She could be very proud, as is common in the Targaryen bloodline. Given the Targaryens' history of dragon - riding and ruling, she would likely have a sense of entitlement. Maybe she's also highly intelligent, using her wits to help Jon Arryn in his political maneuvers.
The 'Game of Thrones' world is vast and full of possibilities in fanfiction. Regarding Jon Arryn's wife in a Blackfyre - related fanfic, it's likely that the fanfic author has crafted a unique story. It could be that the wife is a character who is a part of a secret Blackfyre plot, or she might be a noblewoman from a house that has some connection to the Blackfyre legacy. However, without actually delving into the fanfic, we can only speculate about who she might be.
Perhaps the fanfic could center around a mystery. There could be a secret that Brightflame's wife is hiding, something that Jon Arryn discovers. This secret could be related to her past, or it could be something that has the potential to change the fate of the kingdoms. It might be a prophecy she is aware of, or a hidden identity. As Jon Arryn uncovers this mystery, it could set off a chain of events that shakes the very foundation of the power structure in Westeros. Their relationship then becomes a key element in either saving or destroying the existing order.