One possibility could be a new OC (original character) created by the fanfic author. This character could be a self - taught demolition expert who joins the ninja academy later in life and has to adapt to the ninja ways while also using their demolition skills.
Maybe Rock Lee. He's known for his physical strength. He could be trained in demolition techniques that rely on his brute force. He could use his taijutsu skills to break down walls or structures in a very unique and powerful way, adding a new aspect to his character in the fanfic.
It could be Naruto himself. Imagine if Naruto learned some sort of demolition - related jutsu. He could use it to blow up the hideouts of the Akatsuki or to create new paths in the forest for his friends to travel more easily. His unpredictable nature would make his use of demolition skills quite interesting.
A 'Naruto Demolition Expert Fanfic' could also focus on an existing Naruto character who somehow acquires demolition skills. It could explore how this new ability changes their role in the story. They might start using these skills for strategic purposes, like creating diversions in battles or uncovering hidden passages in ancient ruins by carefully demolishing parts of the structure.
Naruto himself could be the main character in a Shinju fanfic. He has always been about finding new ways to bring peace and understanding. His connection to the nine - tails could play an interesting role if he were to interact with the Shinju. Maybe he could try to convince the Shinju that the ninja world has changed and it doesn't need to be a source of fear and destruction.
Sasuke Uchiha could be a great choice as the main character. He already has a complex backstory and a lot of room for character development. His journey from seeking revenge to finding his own path in the Naruto series can be further explored in a fanfic.
It could be an original character. Maybe a young ninja who discovers their forging abilities by accident. They might come from a small, unassuming clan that has kept the forging secrets hidden for generations. This character would then have to navigate the Naruto world while keeping their newfound power a secret at first, until they realize they can use it to make a difference.
Perhaps Sasuke could be the main character in a different take on a 'hitman naruto fanfic'. He already has his own vendetta and his skills as a ninja could easily be translated into those of a hitman. He has the Sharingan, which gives him an advantage in combat and tracking, making him a formidable assassin - like figure.
It could be a new character that you create specifically for the fanfic. This character could be an outcast from their village because of their strange Koton abilities. They then have to prove themselves and their powers to the others.
Sasuke could also be a main character in such a fanfic. Given his quest for power and his complex personality, his encounter with the Shinigami could lead to some really interesting character development. He might be tempted by the Shinigami's power or be forced to make difficult choices that would change his path.
Rock Lee could be an excellent main character for such a fanfic. Since he already focuses on physical combat in the form of taijutsu, wushu would be a natural extension for him. He could be sent on a journey to learn the true essence of wushu and bring that knowledge back to Konoha to revolutionize the way they think about physical combat.
Sasuke could be a great main character for a swordsman - themed fanfic. Since he already uses a sword - like weapon, the story could focus on his further development as a swordsman, exploring different sword techniques and their origins.
A new villager who has just moved to the village could be the main character. They are intrigued by the Naruto statue and start to have dreams where Naruto seems to be communicating with them. They then embark on a quest to understand what these dreams mean and how the statue is involved.