A character who is a master of shadow puppetry, but not in the normal sense. Instead of just creating simple shapes, they can create entire landscapes and armies of shadow creatures. This character could have a mysterious backstory and their own motives, which could either make them an ally or an enemy in the fanfiction.
A character who is a descendant of an ancient clan that once had a connection to the Nine - Tails could be added. This character could have some knowledge about the Nine - Tails that was lost over time and could help Naruto better understand his power.
There are original characters who are members of a secret ninja clan. They cross paths with Jiraiya and Naruto during their adventures. These characters bring in new ninja techniques and a different culture within the ninja world. Also, there could be a young orphan that Jiraiya and Naruto take in. This character could represent a new generation that they are responsible for, and it adds a new dynamic to the story of Jiraiya raising Naruto.
One common type of original character is a rival. This rival could be another ninja who also wants to harness the power of the Kyuubi, either for good or bad reasons. They might challenge Naruto and his brother at every turn. Another could be a healer who is specifically attuned to the Kyuubi's chakra and can help Naruto when he has trouble controlling it. There could also be an old sage - like character who has been around since the time the Kyuubi was first sealed and has secrets to share.
One type of original character often added is a love interest specifically created for Fem Naruto in the high school setting. This character could be a charming athlete or a smart student council president. Also, there could be a quirky art student who becomes Fem Naruto's friend and introduces her to a whole new world of creativity. Additionally, an over - enthusiastic teacher's assistant might be added as an original character, always getting Fem Naruto into some sort of comical school - related trouble.
You could create a character who is a descendant of an ancient clan that has a special connection to the Nine - Tails Chakra. This character could be a rival to Naruto at first, thinking that Naruto doesn't deserve the power of the Nine - Tails. Another option is a mysterious healer who can manipulate the Nine - Tails Chakra in a unique way to heal even the most severe wounds.
A psychic human. This character could sense the demons' movements and intentions before they attack. They could use their powers to help the Doom Slayer or other marines, for example, by warning them of an ambush or guiding them through a maze - like area filled with demons.
A young artist from a neighboring kingdom could be introduced. He hears about the Beast's castle and is intrigued by the rumors of its beauty and mystery. When he arrives, he could befriend Belle and see the relationship between her and the Beast. His unique perspective as an artist could add a different dimension to the story, like he could paint pictures that somehow affect the curse.
A character like a Pokémon whisperer who can communicate with Pokémon on a deeper level than anyone else. This person could teach Ash new ways to bond with his Pokémon. Another could be a wandering minstrel who travels around the Pokémon world, singing tales of legendary Pokémon and has clues about a powerful Pokémon Ash is seeking.
One interesting type of original character is a wandering ninja who has been on a quest to find the true nature of the Nine - Tailed Fox. This character might cross paths with Naruto and share their knowledge or experiences. Another is a young girl who can communicate with the Nine - Tailed Fox on a spiritual level, which causes Naruto to be both intrigued and a bit jealous. And then there are the members of a secret organization that wants to harness the power of the Nine - Tailed Fox for their own dark purposes, and they create original characters within this organization who have unique abilities and motives.
Maybe Naruto discovers that some of his friends are actually NPCs (non - player characters) but they have developed real emotions. This would create a huge moral dilemma for Naruto. Does he treat them as real friends or just part of the game? It would also add a lot of depth to the story.