The bijuu are the main characters as they are the focus of the 'goes to Yuki Academy' part. However, depending on how the story unfolds, there might be some side characters like the academy's janitor who has some secret knowledge about the bijuu and ends up helping them in unexpected ways, but still, the bijuu are the central figures.
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, he might introduce his unique ninja skills to the Duel Academy. Maybe he'll use his shadow clone jutsu during duels, confusing his opponents. He could also make friends with some of the students there who are interested in his different fighting style.
Well, he might find the whole boarding school thing really strange. Naruto is used to his village life in the Naruto world. At Yancy Academy, he'd probably be the odd one out with his ninja skills and energetic personality. He could get into trouble for using his ninja moves accidentally, like when he tries to jump from one building to another thinking it's normal like in Konoha.
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.