Well, you could write a fanfic where the Ten Tails actually has a conscience and is not just a mindless beast. It could be that it was once a good entity but was corrupted. A young ninja with a special ability might be the key to restoring the Ten Tails to its former self. This would involve a lot of character development and exploration of the Naruto lore.
A great plot could be about a group of young ninjas who accidentally awaken the Ten Tails and then have to find a way to reseal it before it destroys everything. They could discover new jutsus and powers along the way. Also, what if the Ten Tails had a different form that was not known before, and the characters have to figure out how to deal with it.
Well, a possible plot for a 'naruto with tails fanfic' might involve Naruto using his tails to travel to different dimensions. In these dimensions, he could encounter alternate versions of his friends and enemies. He might have to use the unique abilities of his tails to find his way back home. Or perhaps his tails start to develop a mind of their own and he has to work with them rather than against them to become stronger. Maybe he discovers that his tails hold the key to unlocking a long - lost prophecy related to the Hidden Leaf Village.
For a 'naruto of the nine tails fanfic', a great plot could involve the nine - tails sharing its ancient memories with Naruto. These memories could give Naruto insights into the history of the ninja world and new ways to use his power. Additionally, a plot where the nine - tails starts to develop its own emotions and opinions that conflict with Naruto's, leading to an internal struggle for Naruto, would be really interesting.
Another cool plot twist could be that the Ten Tails has the ability to split into multiple smaller entities, each with its own unique power. This would force Naruto and his friends to come up with new strategies to deal with these new threats. And it might also lead to some of these smaller entities turning good and helping Naruto in unexpected ways.
One idea could be exploring the origin of the Ten - Tails in a different light. Maybe it was created by an ancient civilization for a noble purpose that got corrupted over time. Another could be a story where a young ninja discovers a hidden power within the Ten - Tails and has to learn to control it without being consumed by its dark energy.
Well, a cool plot might be that Naruto uses the Nine - Tails to travel to different dimensions. He could explore places that were previously unknown and discover new powers or allies there. Also, in the fanfic, he could use the Nine - Tails' chakra to heal the land that was damaged by previous battles. This would show his growth not just as a fighter but also as a protector of the village and its surroundings.
Perhaps in the fanfiction, the Zero Tails is a manifestation of the negative emotions of the ninja world as a whole. A group of young ninjas discover this and they try to find a way to purify the Zero Tails. They seek the help of old sages and learn ancient jutsu to attempt this purification, which could lead to a battle against those who want to keep the Zero Tails as a weapon of mass destruction.
One idea could be Naruto having a unique connection with the Nine Tails that allows him to access new forms not in the original series. For example, a form that combines his human features with more fox - like aspects in a more aesthetically pleasing and powerful way.
One idea could be exploring the Four Tails' backstory more in - depth. Maybe it has a connection to an ancient ninja clan that was long forgotten. Another is a story where the host of the Four Tails has to team up with an unexpected ally to control its power.
One idea could be a fanfiction where Naruto has to temporarily transfer the Nine - Tails' power to a fellow ninja to save the village. This would create an interesting dynamic as the other ninja has to quickly adapt to the power and the responsibility that comes with it.
A plot could revolve around a Nine Tails that gets separated from its trainer during a storm. It then has to find its way back through a dangerous and unfamiliar territory, facing various other Pokemon and obstacles along the way. This could show the Nine Tails' intelligence and determination.