It could be about Naruto attaining a god - like form related to the bijuu. Maybe he gains incredible powers that are far beyond normal and the fanfiction explores his adventures and battles in that state.
Maybe there's a rogue ninja who has developed a new and dangerous jutsu that can counter Naruto's powers. This ninja wants to prove himself as the strongest by defeating Naruto and taking over the bijuu's power. He might be jealous of Naruto's newfound status and the respect he gets from the other ninjas.
Well, Naruto is the obvious main character. However, depending on the plot, characters like Kakashi could be involved as well. He could be guiding Naruto in handling his godlike powers. And the villains in the fanfiction could also be main characters in a sense, as they would be the ones creating challenges for Naruto in his new state with the godlike bijuu powers.
One interesting plot point could be Naruto having an even more enhanced connection with the bijuu, allowing him to access new and powerful forms. For example, he might be able to combine the powers of all the bijuu in a unique way that no one has ever seen before.
In fanfiction, if Naruto is half - bijuu, it could mean he has enhanced physical abilities. For example, he might have greater strength and speed like a full - bijuu. His chakra reserves could also be much larger, allowing him to perform more powerful jutsu for longer periods.
In many Naruto fanfictions, if Naruto has three bijuu, they could be the Nine - Tails (Kurama) which he already has in the original series, perhaps the Eight - Tails (Gyuki) as it has a connection with Naruto's world and Akatsuki's hunt for the bijuu. And another could be the Three - Tails (Isobu). However, it really depends on the specific plot and creative direction of the fanfiction.
It could be an ancient sage. In Naruto lore, there are sages who have had a great influence on the world. An ancient sage could be the one who created or fathered the bijuu. Maybe he had some great power and knowledge that allowed him to bring the bijuu into existence.
It could be Shukaku. Since Shukaku was one of the first bijuu introduced in the series and has a sand - based power, it would be an interesting addition to Naruto's arsenal. Naruto's positive and energetic personality could also have an impact on Shukaku's usually grumpy and solitary nature.
Well, having two bijuu would likely make Naruto extremely powerful. He could potentially combine their unique chakra natures and abilities in combat. For example, if one bijuu has a fire - based ability and the other has a water - based one, he might be able to create new and unexpected jutsu by mixing them. Also, it would change his standing in the ninja world. People would probably be more in awe or more fearful of him, depending on their stance towards Naruto.
In 'fem bijuu are possessive of naruto fanfiction', Kurama is likely to be a very prominent fem bijuu. Given her power and the fact that she has been inside Naruto for a long time, her possessiveness can really shape the story. Additionally, Matatabi, the Two - Tailed Cat, could also be a notable fem bijuu. Her feline nature might add an interesting layer to her possessiveness towards Naruto, perhaps making her more sly and protective in a different way compared to Kurama.