Perhaps a foreign ninja who comes to the Hidden Leaf Village. They bring with them the scythe - using techniques from their own land. This ninja could be on a mission to learn more about the chakra system in the Naruto world and in exchange, teach their scythe skills. Their different cultural background would add an interesting dynamic to the story as they interact with the local ninjas.
One potential character could be Sasuke. Imagine in a dark, alternate universe fanfic where Sasuke, instead of using his sword, wields a scythe. It could be a symbol of his more menacing and reclusive nature. He might use it with his Sharingan abilities, making his strikes not only powerful but also unpredictable as he can anticipate his opponents' moves.
Jiraiya could be an interesting assassin master. He already has a lot of knowledge and skills that he could pass on to Naruto in a more assassin - like way. His experience in espionage and combat would make him a great fit.
It could be a rogue ninja who was once a student of the Hiraishin master but turned evil. They might have a twisted view of the technique and use it for their own selfish and harmful purposes, like stealing important artifacts from different villages.
One potential antagonist could be a rogue ninja who also specializes in bojutsu. He might be jealous of the main character's skills and tries to undermine him at every turn. Another option is a powerful villain from the Naruto universe who sees the bojutsu master as a threat to his plans.
A new character could be introduced as a Sharingan master. For example, a wandering ninja who has been secretly studying the Sharingan for years. He might have no allegiance to any village and travels around, looking for worthy pupils to inherit his knowledge. He could have unique techniques related to the Sharingan that no one has seen before.
It could be a rogue ninja from a village that specializes in earth - style jutsus. Since futon techniques are weak against earth - style, this enemy would pose a significant threat to the Futon Master. They might target the Futon Master to steal their techniques or to prove the superiority of earth - style over futon - style.
Sasuke could be a rival. He's always been highly skilled and competitive. His Sharingan could potentially see through some of the henge master's henges, creating a constant challenge for the henge master to come up with more advanced henges.
One potential character could be Sasuke. He has always been highly skilled with weapons and his Sharingan would give him an edge in mastering knife techniques. He has the determination and the combat skills to be a great knife master in a fanfiction setting.
Sasuke could be a potential rival. In many Naruto fanfictions, Sasuke is highly skilled in ninjutsu and sharingan - based genjutsu. His rivalry with Naruto, if Naruto becomes a genjutsu master, would be intense. Another could be Itachi. His mastery of genjutsu, like Tsukuyomi, would make him a formidable opponent for Naruto in the genjutsu realm.
The origin could be some ancient, long - forgotten magic. Maybe it was created by a powerful and now - extinct clan. They might have imbued it with a spirit or some form of intelligence for a specific purpose, like protecting a hidden treasure or an important location.