If the spin - off is about the Targaryen dynasty, then characters like Aegon the Conqueror could be the main character. He was the one who led the Targaryen invasion of Westeros with his sisters and their dragons. His story is full of conquest, power - building, and family drama.
For a spin - off about the Night's Watch, a young recruit who discovers some dark secrets about the Watch could be the main character. He could be an idealistic boy at first, but as he uncovers the truth about the Watch's past, its connection to the Others, and the internal corruption, he has to decide what to do. This character would have to navigate a world full of danger and moral ambiguity.
One idea could be a spin - off focusing on the early days of the Targaryen dynasty. We could see how they first came to power in Westeros, their dragon - riding adventures, and the power struggles within their own family. It would be fascinating to explore the origins of their rule and how it set the stage for the events in Game of Thrones.
Well, if the spinoff is about the early Targaryens, then Aegon the Conqueror would be a main character. He was the one who united most of Westeros under Targaryen rule. Another could be Daenys the Dreamer, as she had the prophetic dreams that led the Targaryens to leave Valyria.
Arya Stark could be a main character. She could use her skills as a Faceless Man to infiltrate the enemy's camp before a big battle and gather intelligence. Her ability to change her appearance would give her an edge in spying and sabotage operations during the battle.
It could be Arya Stark as the bodyguard. Given her skills in combat and disguise, she would make a great protector. She could be protecting someone like Bran Stark as he continues to develop his powers and is a target because of his abilities.
The children of the original characters would be likely main characters. For example, Jon Snow's (if he has any) descendants. They could inherit his sense of honor and face new challenges in the post - war Westeros.
You could have a main character who is a commoner. Maybe a peasant girl who witnesses the fall of a great house and has to navigate the chaos that follows. She could get involved with the various factions vying for power, and through her eyes, we see the events of the prequel unfold. This would give a different perspective compared to the noble - centered stories we often see in the 'Game of Thrones' universe.
Gendry could also play a major role. As a skilled blacksmith and a bastard like Jon, he has the strength and the will to fight for change. He could use his skills to arm the revolutionaries and his knowledge of the common people's plight to inspire them to rise up against the unjust noble rule.
A samurai - like character from Zipang could be a main character. They would be skilled in combat and bound by a strict code of honor. They could enter the fray in Westeros and become involved in the power struggles, perhaps even challenging the likes of Jaime Lannister in a duel of honor.
Jon Snow would also make a great main character. He could be on a mission to unite the different houses' spaceships against a common threat, like an alien race or a powerful space - faring pirate group. His leadership skills and sense of justice would be put to the test in this new setting.
There are characters from different noble houses. For example, members of House Forrester are among the main ones.