It might also be Naruto himself in an alternate universe or a different time in his life. Even though Naruto is a strong character in the original story, in this fanfiction, he could be facing new challenges that make him feel like he's on the verge of becoming 'trash' if he doesn't fight back. So he makes this vow to not let that happen and to keep on growing and becoming stronger.
Perhaps it's a minor character from the original Naruto series who decides to step out of the shadows and prove that they're not just a nobody. For example, someone like Tenten who wants to show that she can be as great as the more prominent ninjas. They see the potential for themselves to be more than just 'trash' in the highly competitive ninja world.
I'm not sure specifically as I haven't read this exact fanfiction. But generally, it might be about a character in the Naruto universe vowing not to become useless or 'trash'. It could be about their journey to gain strength, prove themselves, or avoid a certain fate that would make them seem like a failure in the eyes of others.
It could be a character who is an anti - hero from the 'gangsta' series. They might have a tough exterior but a soft heart inside, and the 'i won't hurt you' line could be part of their redemption arc in the fanfiction.
The author of 'Stars Won't Turn' was He Fei.
It could be an ordinary middle - aged person who is dissatisfied with their current life. Maybe they have a boring job and a failing marriage, and turning back time is their chance to start over.
It could still be Naruto himself, just with a focus on a different, smaller part of his life or personality.
It could also be a young apprentice of the shopkeeper. This character could be learning the ropes of running the shop while also having dreams of becoming a great ninja. They would be in a position to interact with both the regular customers of the shop and the more famous ninjas, which could lead to all sorts of interesting storylines.
It could be Megaman himself. He could be transported to the Naruto world and have to adapt to the new environment while using his skills to make a difference. His sense of justice would fit well in the Naruto universe.
It could be an original character created specifically for the fanfiction. Maybe a rogue ninja with a vendetta against the Hidden Leaf Village.
Naruto himself could be the main character. Imagine Naruto getting his hands on a special pistol - like weapon and having to learn how to use it while still relying on his normal ninja skills. It would be a new challenge for him and could lead to some great character development as he tries to master this different form of combat.
Naruto himself could still be the main character. He might be faced with a situation where he has to make difficult choices to prevent carnage, and in the process, his character could develop in new and unexpected ways, like having to use more ruthless tactics.