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.
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.
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.
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.
In Tywin Lannister x Sansa fanfiction, a frequently seen theme is the transformation of Sansa. Under Tywin's influence, she could be transformed from a naive girl into a more politically astute woman. Also, the theme of loyalty is important. Sansa's loyalty to her family and her house is put to the test when dealing with Tywin. Will she stay true to her Stark roots or be swayed by Tywin's offers? Additionally, the theme of revenge can come into play. Sansa may seek revenge against the Lannisters for what they've done to her family, and her relationship with Tywin can be a part of that revenge plot, either by using him or by directly opposing him.
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.
There's also 'Tywin and the Unlikely Apprentice'. In this fanfiction, the OC is a young orphan with a unique skill set. The story delves deep into how Tywin's relationship with this character unfolds over time. It shows his calculating nature as he tries to use the OC to his advantage, but also how the OC manages to influence him in unexpected ways. This fanfiction is really good at exploring the complex personality of Tywin Lannister.
To develop the character, consider his backstory. What was his childhood like? Did he have a special tutor or mentor? His experiences outside the Lannister stronghold are also crucial. If he travels and meets different people, it can change his views. For instance, if he meets a group of poor peasants and sees their struggle, it might make him more empathetic. Also, his moral compass can be different from his father's. He could be more inclined towards justice and fairness, which would lead to conflicts within the family.
One idea could be the daughter getting involved in the political intrigues of King's Landing. Maybe she has to navigate the complex relationships between the different houses while trying to uphold the Lannister name. Another could be her having a secret talent, like being an excellent strategist, which she uses to help her father in unexpected ways.
One idea could be the OC's struggle to live up to his father's reputation. He might face challenges within the Lannister family, like dealing with his siblings' envy or rivalry. Another could be his role in the political games of Westeros, perhaps trying to form alliances different from his father's.