One possible plot could be that Jaime uses the magic hand to gain new combat abilities. He might be able to deflect arrows or even send out energy blasts from the hand.
It could be a powerful sorcerer who wants to take the magic hand for himself. This sorcerer might see Jaime as an unworthy holder of such a powerful artifact and will stop at nothing to get it.
Sure, many fanfiction authors like to play around with different character combinations and scenarios. Jaime Lannister is a complex character, and Lyanna has her own allure in the story. The idea of her being pregnant in a fanfiction involving Jaime could be used to explore themes like love, honor, and the consequences of actions. It might show how these two characters from different houses and storylines interact in such a situation.
In some fanfictions, Jaime could receive magic that is linked to his golden hand. Maybe it has some sort of enchantment that allows him to sense danger or even project a shield. This would add a whole new dimension to his character. He would have to adapt to this new aspect of himself while still dealing with the politics and relationships in the Seven Kingdoms.
A great one might be 'Jaime's Magical Redemption'. In this, Jaime gets magic that helps him atone for his past sins. He uses his magic to help the common people, which is a big change from his previous self - centered actions. It's a story that really delves into his character development with the added element of magic.
Power and politics often play a big role. Just like in the original series, the Lannisters are all about power. In fem Jaime fanfiction, she is usually involved in political machinations, whether it's trying to hold onto the family's power or break free from it. Also, relationships are a major theme. Her relationships with family members like Cersei and Tyrion are explored in new ways, as well as potential romantic relationships.
I really liked 'Jaime Lannister: A Different Path'. In this fanfiction, Jaime decides to side with the Starks early on. It's an interesting take as it completely changes the course of his character in a believable way. There are some great character interactions that are not in the original show.
Well, perhaps in the fanfiction, Jaime discovers Lyanna in a difficult situation and feels compelled to protect her. As they spend time together, feelings develop, and Lyanna becomes pregnant. The plot could then revolve around them trying to keep the pregnancy a secret from those who would use it against them. It could also explore how their relationship affects the overall power dynamics in Westeros, with different factions trying to manipulate the situation for their own gain. There could be a lot of internal conflict within Jaime as he struggles with his past actions and his new role as a potential father and protector of Lyanna.
One great fanfiction could be one where Jaime and Brienne go on a quest together after the main events of the series. It might explore their relationship deeper as they face various challenges. They could encounter enemies from both their pasts and have to rely on each other's skills.