Well, Lord Eddard Stark could interact with Gared. Given that Eddard is a nobleman of the North, he might cross paths with Gared, perhaps when Gared was still in the North before joining the Night's Watch. They could have conversations about the state of the North, the rumors of strange things in the far North, which could be an interesting dynamic as Eddard is a man of honor and Gared is just an ordinary man with his own fears and hopes.
Samwell Tarly could also be a character to interact with Gared. Sam is a bit of an outcast in the Night's Watch like Gared might have been. They could bond over their feelings of being different from the other members. Gared could have given Sam some advice on how to survive in the harsh environment of the Wall, and Sam could have shared his knowledge from his studies with Gared.
One idea could be exploring Gared's backstory before he was in the Night's Watch. Maybe he had a family or a love interest in his village that he left behind.
One main character could be a genetically - enhanced human who has special abilities, like Arya Stark's skills in the original. She could be on a mission to avenge her family who were killed by a powerful space - faring clan. There could also be a powerful warlord from a distant star system, a bit like Ramsay Bolton, feared for his cruelty and thirst for power. The interactions between these diverse characters would drive the story forward in this space - based Game of Thrones fanfiction.
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.
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.
If he met Jon Snow, Loki might be intrigued by his half - wild, half - noble nature. He could either try to use Jon for his own purposes or see him as an ally against the greater threats in Westeros.
The children of Sansa Stark and Tyrion Lannister would be interesting main characters. They would have a unique heritage, being part Stark and part Lannister. Their story could be about bridging the gap between the North and the South, facing the challenges of being accepted in both regions. They might have to deal with the political unrest that still lingers after the events of the original series, while also trying to create a better future for themselves and Westeros.