Often, there's a plotline where the OC is a servant or a low - born character who rises to prominence and has to deal with the politics of Tywin Lannister and the Starks. They might be caught in a web of lies and intrigue as they try to serve both sides without getting killed. Also, a plotline could involve an OC as a mage or a seer who foresees the destruction that the feud between the two houses will bring and tries to stop it.
A prevalent plotline in such fanfiction is the OC falling in love with a member of either the Lannister or Stark family. This love story then becomes intertwined with the larger political and family drama. For example, an OC might fall in love with a Stark son while also having to deal with Tywin Lannister's schemes against the Starks. Or an OC could be a Lannister girl who falls for a Stark, and they have to fight against the prejudices and enmity of their families. There are also plotlines where the OC is an assassin hired to kill a key member of either family, but then has a change of heart due to unexpected interactions with the family members.
Well, in some fanfictions, Sansa might learn from Tywin about power and leadership. Since Tywin is a master of political intrigue, Sansa could start to pick up on his strategies. For example, she could use his teachings to gain more influence in the court, while also trying to keep her Stark identity intact. This would create an interesting dynamic between them as she tries to navigate the dangerous world of the Lannisters.
In OC fanfiction involving Tywin Lannister and the Starks, Tywin's strategic mind is a central aspect of his portrayal. He is always looking for ways to strengthen his house's position. The Starks, on the other hand, are known for their integrity. An OC could be a healer, for instance, who treats the wounded from both sides during a battle. This OC's presence might lead to some unexpected interactions between Tywin and the Starks, like Tywin seeing the Starks in a more sympathetic light due to the OC's influence.
Some fanfictions have a plot where the OC has some knowledge or ability that Tywin wants to use for his own gain. As they work together, feelings start to develop. There might also be a plot where the OC is from a rival family, and their relationship is a secret that could have major consequences if discovered, adding a lot of suspense to the story.
Power is a very common theme. Since Tywin is all about power in the original story, fanfictions often explore how he gains, maintains, or loses power in different scenarios. Family dynamics is another one. His relationship with his children, especially Tyrion, Jaime, and Cersei, is always a rich area for exploration in fanfictions.
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.
A plotline might involve Sansa trying to protect her unborn child from the dangerous political games in Westeros. With Tywin as the father, the child would be in the middle of many power plays. Also, there could be a plot where Sansa uses the pregnancy to try and change the Lannisters' attitude towards her and her family. Maybe she hopes to bring some peace between the Starks and the Lannisters through the child. It could also explore how Tywin would react to having a child with Sansa, considering their different backgrounds and ages.
In such fanfiction, the relationship can be complex. Tywin Lannister is a complex character. An OC (Original Character) might be drawn to his power and authority at first. But his cold and calculating nature could also create conflict. For example, the OC might try to humanize him, which would be a difficult task considering his reputation.
The novelty of original characters. They can bring new perspectives to the world of Tywin Lannister. For example, an OC could be from a different social class and show us how Tywin interacts with those he normally wouldn't deal with.
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.