One possible fanfiction could start with Robert Baratheon as a young man. He is full of ambition and dreams of a united Westeros under his rule. He trains hard in combat, his sword becoming an extension of himself. He meets his future friends, like Ned Stark, during these formative years. They share tales around the campfire and make grand plans for the future. As he grows older, he participates in battles, his victories making him more and more renowned. His charisma draws people to him, and soon he is seen as a natural leader. But with power also comes temptation, and he has to face the challenges of politics and intrigue that come his way.
To make a fanfiction about Robert Baratheon interesting, you can give him new challenges. Maybe he has to deal with a magical threat that the original series didn't show him facing. You could also explore his backstory more. What was his life like before he became king? His upbringing, his first loves, and his early battles could all be interesting areas to explore. Additionally, changing the power dynamics around him can be great. For instance, if some of the minor houses suddenly become more powerful and he has to negotiate with them. This can lead to all sorts of interesting political intrigue and character development.
She could also be shown as a great warrior in certain fanfictions. Despite the norms of the society in Game of Thrones that often restrict women's roles in combat, she breaks free from those constraints. She trains in secret and then emerges as a surprise defender of her family when they are under attack.
Another aspect that fanfictions often explore is her relationship with other members of the Baratheon family. In some stories, she could be at odds with Cersei, seeing through her false charm and manipulative ways. This creates a power struggle within the family, which is a common and engaging theme in Game of Thrones fanfiction.
One interesting fanfiction could be one where Renly Baratheon survives and forms a different alliance. Maybe he teams up with the Starks against the Lannisters, which would completely change the power dynamics in Westeros.
Love and loyalty also feature prominently. An OC Baratheon might be torn between loyalty to their family and their love for someone from another house. This creates a lot of internal conflict and interesting plotlines. In some stories, an OC Baratheon's loyalty to a friend or a romantic partner can change the course of events in the political landscape of Westeros.
Perhaps their relationship begins with curiosity. Daenerys has heard of the powerful Robert in Westeros, and Robert is intrigued by this Targaryen with a claim to the Iron Throne. As they communicate more, they find common ground in their desire for a just Westeros. They might start to fall in love slowly as they share their dreams and fears, and work towards building a better future for the Seven Kingdoms.
There might be a fanfiction where Tommen discovers a hidden power within himself. For example, he has the ability to communicate with animals. This new power helps him to better understand the needs of his people and make more informed decisions as king. He could use this power to gain the loyalty of his subjects in a unique way.
Well, one way could be through a magical portal. Imagine Naruto, with his ninja skills, suddenly appears in the world of Westeros. His abilities like shadow clones could be mistaken for some dark magic in the Game of Thrones universe. He might team up with the Baratheons, perhaps using his skills to help them in battles, especially against the White Walkers if we're thinking of a scenario where he arrives during that threat.
The male OC Baratheon could also be a bastard son who has been living in exile. He returns to Westeros with a group of loyal followers he has gathered over the years. His main goal could be to claim a small piece of land for himself and his men, but he soon realizes he has to navigate the complex web of politics and allegiances in order to survive.