Consider their upbringing. If they were raised away from the main Lannister stronghold, they might have a different set of values. Maybe they were raised by a kind - hearted servant who taught them to be more empathetic. So their personality could be a mix of Lannister pride and this new - found empathy. They could be conflicted between loyalty to their family and doing what is right according to their own conscience.
Power is a common theme. Since the Lannisters are known for their thirst for power, many 'oc lannister fanfiction' stories revolve around how an oc deals with power within the family. Another theme is loyalty, whether it's the oc's loyalty to the Lannister family or the loyalty of the family members to each other.
If the male OC Lannister was a proud and ambitious type, he would likely interact with Cersei with a mix of respect and rivalry. He'd try to gain her favor while also making sure she didn't see him as a threat. With Tyrion, he might initially look down on him but later come to respect his intelligence. And when it comes to Jon Snow, he could start off as dismissive but as he realizes Jon's leadership skills, he might try to form an alliance.
One great 'Jaime Lannister OC Wife Fanfiction' is 'The Lion's Bride'. It delves deep into the relationship between Jaime and his original character wife. The story shows how she changes his perspective on life and honor in the complex world of Westeros.
Love and friendship are also common themes. The oc might form a deep emotional bond with Jaime, whether it's romantic love or a strong friendship. This bond can help Jaime grow as a person. In some fanfictions, their relationship is what gives Jaime the strength to face his demons. Another theme could be power dynamics. Jaime comes from a powerful family, and the oc's relationship with him can either disrupt or reinforce those power structures.
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.
To develop the male OC, start with his goals. Maybe he wants to gain power and sees Cersei as a means to that end. His appearance can also play a role. If he has a striking look, it might attract Cersei's attention. His relationships with other characters are crucial too. If he has a close friend or mentor, they could influence his actions towards Cersei. For instance, if his mentor warns him about Cersei's dangerous nature, he has to decide whether to listen or pursue his own desires.
One common theme is family dynamics. Genna is part of the Lannister family, so exploring her relationships with other family members like Tywin or Jaime is popular. Another theme is her role in the political intrigue of Westeros. Writers often delve into how she might have influenced events or been affected by them.
You can start by looking on Archive of Our Own (AO3). It has a large collection of fanfictions, and there are likely many Cersei Lannister OC ones there. Just use the search function and type in relevant keywords.
There's also 'Cersei and the Unknown Heir'. In this fanfiction, the OC is a supposed heir to a powerful house and how Cersei deals with this threat and possible alliance is the focus. It's full of political intrigue which is typical of Cersei's storylines.