It's hard to tell without reading it. However, it might introduce new characters that interact with the well - known ones. It could be a story about a commoner who becomes important because of a timely action. But it's also very likely that the main characters are the ones we already know from the original series. For instance, Arya Stark could be a main character if the fanfic is about her exacting revenge at a crucial moment, which would be in line with the 'stitch in time' idea of taking action at the right time.
Since the title is rather open - ended, the main characters could be anyone from the vast 'Game of Thrones' universe. It could be a story about the Night King if the 'stitch in time' refers to someone trying to stop his advance before it's too late. Or it could be a story about Sansa Stark and her journey, where she makes a key decision at just the right time. There are so many characters in the 'Game of Thrones' world that the fanfic writer could have chosen from.
Well, it could revolve around a particular event in the 'Game of Thrones' universe where someone uses their wits or skills just in time. Maybe it's a story about a character who seizes an opportunity at the right moment to gain power or save someone they care about. For example, a character might step in to stop a betrayal just before it's too late, similar to how a stitch in time saves nine in real - life situations. It could also be a more fantastical take, like using magic at a crucial moment.
There are various types. Some might focus on alternate timelines or character development that wasn't explored in the original show.
There could be a young, ambitious knight who has seen the injustices in the Seven Kingdoms and becomes a key figure in the uprising. Another might be an old and wise maester who secretly supports the uprising and uses his knowledge to help the rebels. Also, a strong - willed noblewoman who has her own reasons for wanting change could be one of the main characters.
There's no way to know exactly without reading it. However, in a 'Game of Thrones' - themed fanfic with 'no mercy' in the title, it's likely to have some of the fan - favorite characters in key roles. Maybe Arya Stark, with her assassin skills, could be a main character, showing no mercy to those on her kill list. Or it could be Cersei Lannister, being even more merciless in her quest for power and revenge than she was in the original series.
In some versions of 'a stitch in time story', there might be a craftsman as one of the main characters. He notices a small flaw in his work, say a tiny crack in a pot he is making. And then there could be his master or an old experienced colleague who emphasizes the importance of fixing it immediately. So the main characters are usually someone facing a small issue and someone guiding them to solve it promptly.
I think Naruto would be like the central hero, similar to how Daenerys was in Game of Thrones. He wants to bring change and justice. Then there's Kakashi, who could be like a wise advisor, much like Tyrion Lannister in some ways. And Gaara, with his past of being an outcast, could be a character who rises above his circumstances, just like Theon Greyjoy did at some points.
There might be a Stark character as well, since in 'Game of Thrones' the Starks are often associated with wolves. They could be intertwined with the Black Wolf's story, perhaps as its protector or someone it protects.
The main characters could also be entirely new characters introduced in the fanfic. The author might create someone who has a unique connection to the events of the original series and is given the task of changing things. However, it's also possible that classic villains like Cersei could be main characters if the fanfic is about giving her a second chance at ruling, perhaps with a different approach this time.
There might be a new character introduced in the fanfic. This character could be a commoner who has a special connection with the dragon. For example, a shepherd who once saved the dragon when it was a hatchling and now the dragon has returned to repay the kindness. This character then gets involved in the high - stakes politics of Westeros because of their relationship with the dragon. Another main character could be a powerful lord or lady who sees the dragon's return as a threat to their power and will do anything to stop it or control it for their own gain.
There could be a fearless space captain as one of the main characters. He or she might be leading a group of rebels against a tyrannical interstellar regime, much like how some characters in 'Game of Thrones' fought against unjust rulers.