Maybe an outcast ninja. This person has always been on the fringes of the ninja society. Discovering the neglected sword gives them a chance to prove themselves. They could be someone with a lot of untapped potential who uses the sword to rise above the neglect they've faced.
A ronin - like character in the Naruto world could be the main character. They don't belong to any particular village or group. When they find the neglected sword, it becomes their most precious possession. They embark on a journey to restore the sword's glory and in the process, they become a force to be reckoned with in the Naruto universe.
It could be a young and ambitious Kiri ninja who has grown up seeing the neglect of his village. He might be determined to change the situation and prove that Kiri is not to be underestimated. Maybe he has a special jutsu or ability that he believes can put Kiri back on the map.
It could be Samehada itself. Since the story is about it being neglected, it makes sense for it to be the main focus. It could have its own 'voice' and thoughts as it tries to deal with the situation.
It could be a new character created specifically for the fanfiction. Maybe a young ninja who discovers the neglected dragon and forms a bond with it.
It could be an orphan who has a natural talent for music but has been brought up in a ninja - dominated environment where music is seen as a useless skill. So, they are constantly neglected.
It could be an unknown Uchiha who was overlooked in the main story. Maybe they were born with the Rinnegan but due to some political unrest in their village, they were forced to hide their power and were thus neglected. In the fanfiction, they could come out of hiding and shock everyone with their Rinnegan - based abilities.
It could be a young Saiyan who was sent to the Naruto universe as part of some sort of experiment by the Saiyan race. They are neglected because they seem so different from the ninjas. They would be the main character as they struggle to find their place and purpose in this new world.
A young and talented Iwa ninja who feels left out could be the main character. He or she might be frustrated with how their village is always in the shadow compared to Konoha and wants to change that perception.
Well, it could be a symbol of Naruto's outsider status in his family. Maybe the sword was once an important heirloom but was neglected because Naruto was different or not fully accepted. It might hold some hidden power that only Naruto can unlock later, tying into his journey of self - discovery and proving himself.
Well, it could be about a sword that has some sort of hidden power. Maybe it was once used by a great shinobi in the Naruto world but has been forgotten over time. The story might follow a character who discovers the sword and tries to unlock its potential while everyone else in the Naruto universe is neglecting it.
Another option for the main characters could be Kaiba from Yugioh. His pride and determination would make for an interesting dynamic when faced with the neglect from the Naruto world. And from Naruto, Sasuke could be involved. He might initially see the Yugioh characters as a distraction from his own goals, but later on, things could change.