Since the title mentions Naruto and his broken spirit, he's bound to be a central figure. But it's possible that the fanfiction focuses on the impact of Naruto's broken spirit on those around him, making his friends and comrades main characters too. For example, Sasuke might be portrayed as having to come to terms with a broken Naruto, and his journey to understand and help Naruto could be a major part of the story. Also, characters from Naruto's family, if they are brought back in some way in the fanfiction, could also be key characters in this narrative.
If it's about Naruto's broken spirit, Naruto is surely a main character. However, new characters created by the fanfiction author might also be important. They could be villains who intentionally target Naruto's spirit or allies who try to heal him. Additionally, characters like Jiraiya might appear if the story delves into Naruto's past traumas and how they contribute to his broken spirit.