Definitely Hinata is a main character. Given that it's a Naruto - related fanfiction and it has 'to the past' in the title, it's possible that older versions of known characters could be main characters too. For example, the younger versions of Naruto's teachers like Iruka Sensei might be important characters. Also, characters from Hinata's past, like her mother (if she's introduced in the fanfiction), could be main characters as well, as they could be related to the events that Hinata is going to experience in the past.
Based on the title, Hinata is surely one of the main characters. And since it's related to Naruto, Naruto himself is likely to be an important character as well. There could also be other characters from the Naruto universe, like characters from Hinata's clan such as her father or sister, who might play significant roles in the story as it involves Hinata's journey to the past.
Well, from what we can tell, Hinata is the central character as the title starts with 'legend of hinata'. Naruto is also likely to be a main character as the title mentions 'a naruto'. In addition, there might be antagonists or supporting characters from the Naruto series. For instance, characters like Sasuke could potentially be involved, either as an ally or an obstacle in Hinata's journey to the past, depending on how the author writes the fanfiction.
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