Maybe the two individuals who are getting married actually fall in love against all odds. But there are external threats, like a new enemy emerging that tests their loyalty to each other and their respective houses. This could create a situation where they have to choose between their love and their family duties.
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.
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.
Well, it could shift the balance of power quite a bit. The Lannisters are known for their cunning and wealth, while the Starks are respected for their honor and military strength. If they join forces through marriage, other houses will likely be worried. For instance, the Boltons might feel threatened as the combined might of the Lannisters and Starks could easily overpower them.
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.
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 plot idea could be that Tywin, seeing Sansa's value as a political pawn, decides to use her in a different way than originally planned. Instead of marrying her off to Tyrion, he takes her under his wing to teach her the ways of politics in Westeros. This could lead to an unlikely bond between them as Sansa tries to navigate the dangerous world of the Lannisters while still holding onto her Stark identity.
One plot idea could be Arya, in disguise, getting close to Tywin as a servant in King's Landing. She could overhear his plans and use that knowledge to try and undermine the Lannisters from within. Another could be a scenario where Tywin discovers Arya's true identity but decides to keep her alive for some strategic reason, perhaps to use her as a bargaining chip against the Starks. And a third idea might be a story set in an alternate universe where Arya and Tywin form an unlikely alliance against a common, greater threat, like a White Walker invasion in the south before the events at the Wall.
Another plot twist could be that Naruto's own chakra has an unexpected effect on the vampire. Perhaps it changes the vampire in some way, either making them more powerful or causing some sort of internal struggle within them. This would then have a big impact on their relationship as they both have to figure out how to deal with this new situation.
A plot twist could also be that Temari discovers a long - lost relative who has a dark past and tries to use Naruto's influence for evil purposes. Temari would be torn between family loyalty and her love for Naruto, and Naruto would have to help her make the right decision while also protecting their relationship and the villages.
Well, it could be that Hermione is under a spell when she marries Rowle. The fanfiction could then revolve around how she breaks the spell and what she does after realizing she's been forced into this marriage. She might find that Rowle has some redeeming qualities despite the situation, and they could either part ways amicably or decide to work on a real relationship.