They could meet at a grand tournament. Tournaments are common in the Game of Thrones world and attract nobles from all over. Rhaenyra could be there representing her house, and the Stark could be there to prove his worth. They might catch each other's eyes during a joust or some other event.
One possible plot twist could be that the Stark she marries has a secret power or ability. Maybe he can communicate with animals like some Starks in the lore. This would add an interesting dynamic to their relationship as Rhaenyra comes from a different world in terms of magic and abilities. It could also lead to political intrigue as other houses might be jealous or fearful of this union and the new powers it could bring.
The plot might focus on cultural clashes. The Lannisters and the Starks have different values and ways of life. In this fanfiction, it could show how the Stark oc (original character) tries to adapt to the Lannister way of life in Casterly Rock or how Tywin has to deal with the more 'northern' Stark traditions that his new wife adheres to. For example, the Stark oc might be more in tune with nature and the old gods, which could be a contrast to the Lannister's more materialistic and power - hungry ways.
Another theme is the redemption of Tony. Wanda has had her issues with Tony in the MCU, but in fanfiction, their relationship can be a way for Tony to redeem himself in her eyes. It could be through acts of kindness or by changing his ways a bit to be more in line with what Wanda values.
Perhaps the plot could involve the two coming together to fight a common enemy. The Targaryen might bring her dragons (assuming this is in a universe where dragons exist in this fanfiction) and Ned Stark could bring his military might and the loyalty of the North. Their marriage could be a strategic alliance that was initially arranged for political reasons but then they grow to love each other. They would then have to navigate the power struggles in Westeros, with many houses vying for control.
One potential plot twist could be that the marriage is a political move to end a long - standing feud between the two houses. However, there are secret alliances within each house that oppose the union, leading to internal power struggles. For example, some Lannisters might be against sharing power with the Starks, and vice versa.
The plot could center around the cultural clash between the two families. The Lannisters are known for their cunning and wealth, while the Starks are more about honor and loyalty. So, when a Lannister marries Ned Stark, there would be a lot of adjustments. The Lannister in the marriage might try to bring in their lavish lifestyle, which could be resisted by Ned Stark at first. But over time, they could learn from each other. The Lannister could become more honorable, and Ned Stark could understand the importance of some political maneuvering.
At first, it could be very tense. Tywin is used to being in control and having things his way, and the Stark oc would likely have her own ideas and values. So, they might start off butting heads. But as time goes on, they could start to understand each other better. The Stark oc might see that Tywin has his reasons for his actions, and Tywin could come to respect the Stark oc's strength and integrity.
Well, Ned Stark is a given. For the Targaryen side, it could be a Targaryen who has lived in Essos and has different views from the main Targaryen line we know in the books/show. This character could be more open to the ways of the North. Or it could be a young Targaryen heir who Ned Stark marries to strengthen an alliance between the North and any remaining Targaryen supporters. This character might be inexperienced in the ways of Westeros politics and Ned would have to guide her.
Their relationship might start off very rocky. Given the history between their families, there would be a lot of mistrust. But as they spend more time together, they could start to see each other's good qualities. For instance, Ned Stark might notice the Lannister's intelligence, and the Lannister could come to admire Ned's integrity.