It's possible that the black sword has a connection to some ancient prophecy. Naruto is often involved in things related to prophecies. The sword could be a key element in fulfilling a certain prophecy, and it was fated to come into his possession. For example, it might be the only weapon capable of defeating a new and powerful enemy that the prophecy foretells.
Sasuke could be a great wielder. His natural affinity for lightning - based jutsu and his determination would make him a formidable user of the Black Lightning Sword. He could integrate the sword's power into his existing combat style, creating new and powerful attacks.
The sword could have the ability to cut through any chakra - based attacks. Since Naruto's world is full of ninjas using chakra, this would be a very useful ability. It would allow Naruto to easily defend against and counter his opponents' attacks.
There's a fanfiction called 'Black Sword Wielder'. Here, a new character arrives in the Naruto world with the black sword. This character is initially seen as an enemy, but as the story progresses, it's revealed that they are actually trying to protect the sword from a much greater evil. The story has exciting battles and a complex web of relationships between the new character, Naruto, and the other ninja.
In Naruto fanfiction, the Kusanagi sword often takes on a significant role. It might be a powerful weapon that Naruto discovers and has to master. For example, it could be hidden in an ancient temple and Naruto, through his adventurous spirit, stumbles upon it. Then he has to learn how to use it in combat against new and powerful enemies.
Perhaps in the fanfiction, the Black Lightning Sword was created by a long - forgotten clan. The main character, who is an outcast in his village, stumbles upon the sword. With it, he begins to train and master the black lightning powers, all while trying to prove his worth to the village that once shunned him. He could also form an unlikely alliance with a former enemy because of the sword's existence.
He could find it in an ancient, hidden temple during one of his missions. Maybe he was exploring a long - forgotten ruin and stumbled upon the sword, completely by accident.
One interesting Naruto fanfiction with a black sword could be about a new character who wields the black sword and has a mysterious origin. This character might enter the Naruto universe and cause a stir among the existing ninja clans. They could be on a quest related to the sword's power, and the story could involve battles with Naruto and his friends as they try to figure out if this new person is a friend or foe.
Well, I really like 'Sword of the Shinobi' in the Naruto sword fanfiction world. It delves deep into the idea of how a special sword can change the power dynamics in the Naruto universe. The battles are really well - written, especially those involving sword techniques. Then there's 'Bladebound Naruto' where Naruto himself gets a magical sword that has a mind of its own. It's a really interesting take on how Naruto would adapt to having such a powerful and somewhat unruly weapon. There's also 'The Swordsman's Path in Naruto' which follows a side character who decides to become a master swordsman in the Naruto world.