Kabuto could also be a good antagonist. After he gained all those powers and knowledge, he might target Naruto's six - tails form. He could use his medical ninjutsu to try and manipulate Naruto's transformation or even try to extract the power of the six - tails for his own use. Since he has the ability to mimic other ninja's techniques, he could be a formidable foe against Naruto in six - tails form.
Well, a cool plot for Naruto six - tails form fanfiction might be about time travel. Naruto accidentally travels back in time while in six - tails form. He then has to figure out how to hide his form from his younger self and the people in the past. At the same time, he could use his knowledge from the future and the power of the six - tails to prevent some great disasters from happening in the past, which would change the future in unexpected ways.
Naruto could use his Four Tails form to fight a new and powerful enemy that the normal ninja of the Hidden Leaf can't handle. For example, an enemy with the ability to nullify regular chakra attacks.
No. Fanfiction should be about positive exploration of characters and their stories. Abusing a character like Tails is unethical and not in the spirit of fanfiction.
One idea could be a story where Naruto has more control over his Four Tails form earlier than in the original series. He could use it to protect the Hidden Leaf in a new and unexpected way, perhaps by combining it with some new jutsu he's created on his own.
Sakura could be a great choice. She has strong medical ninjutsu skills and a no - nonsense attitude. She could help the six - tails jinchuriki when they get injured during battles against the power of the six - tails or external enemies. Also, her growth as a character could be further explored as she tries to understand and support the jinchuriki.
One idea could be the six - tails jinchuriki's struggle to control the power. For example, they constantly have to battle the inner urge of the six - tails to go on a rampage. Another plot could involve the jinchuriki being hunted by an evil organization that wants to extract the six - tails' power for their own malicious use. They would then have to fight and outwit this organization while also dealing with the social ostracism that often comes with being a jinchuriki.
In certain fanfiction, Naruto is indeed the Ten - Tails. This could be a really cool concept as it combines Naruto's already powerful nature with the ultimate power of the Ten - Tails. It might lead to stories where Naruto has to struggle with the dark side of such power, or he could use it to bring about a new era of peace in the ninja world. Maybe he would have to face off against old enemies who are now even more afraid of his new - found strength.
Well, having six arms would give Naruto more options in combat. He could use multiple jutsus simultaneously. For example, he could form Rasengan in three hands while using shadow clones with the other three to distract his opponents. This would make him more unpredictable and powerful in battles.
Character development can be shown through Naruto learning to control the Nine - Tails' power more precisely. For instance, at first, he might struggle and the power might be wild. But as the story progresses, he can gain more finesse, which shows his growth. Another way is his relationship with the Nine - Tails itself. If he starts off seeing it as just a power source and then comes to understand it as a sentient being with its own feelings, that's great development.