A different plot might be about the Sannin's individual dreams and how they started to diverge. Tsunade's desire to heal and protect, Jiraiya's aspiration to write a great novel and find the child of prophecy, and Orochimaru's thirst for power and knowledge. You could show the events that led to these different paths and how they affected their relationships.
A great plot for 'naruto sannin era fanfiction' would be to show how the Sannin's different ideologies started to form. Orochimaru's thirst for power might have begun with a particular event or discovery during this era. Tsunade could be shown dealing with the loss of her loved ones and how that shaped her views on life and the ninja world. Jiraiya's idea of finding the 'Child of Prophecy' might have been seeded during his experiences in the Sannin era as well.
One idea could be the new Sannin facing a powerful new enemy that threatens the entire ninja world. They have to combine their unique skills, like one being a master of genjutsu, another of taijutsu, and the last of ninjutsu, to overcome it.
One idea could be exploring how the fourth sannin, if there was such a concept, might have influenced Naruto's training in a unique way. Maybe they had a special jutsu that they passed on to Naruto secretly.
Well, a really interesting plot could be that the Sannin were actually working together secretly to protect Naruto all along. They knew something about his birth that made him a target. So, Naruto grows up thinking he's just an orphan with no real connection to them, but as the story unfolds, he discovers the truth. He then has to learn how to use the combined knowledge and powers of the Sannin to face a new and powerful enemy that has been after him since his birth. This would add a whole new layer of mystery and power - up to Naruto's character.
One idea could be that the puppet sannin create a super - powerful puppet that requires the combined skills of Naruto and his friends to defeat. Maybe this puppet has the ability to absorb chakra and uses it to grow stronger.
One idea could be focusing on a young shinobi from a minor clan who discovers a long - lost clan technique during the clan wars. This technique could give their clan an edge but also draw the attention of more powerful clans. Another could be a love story between shinobi from opposing clans, with their relationship being tested by the chaos of the clan wars.
One plot idea could be that the Sannin discover a prophecy that only Naruto, Sasuke, and Sakura can fulfill. So they take the three under their wings more intensively. Jiraiya focuses on Naruto's spiritual growth, Orochimaru on Sasuke's control over his dark powers, and Tsunade on Sakura's physical and mental strength. As they train, they also uncover secrets about the ninja world that could change everything.
Well, one interesting concept could be the new abilities the characters might have. Maybe they develop unique jutsu that combine different elements in unexpected ways. Another could be the relationships between the new sannin, whether they have rivalries or strong bonds of friendship like the original sannin.
Well, it could be that Naruto gets super powerful training from each of the Sannin. Jiraiya might teach him more advanced toad jutsus and how to better control his chakra. Tsunade could train him in medical ninjutsu and physical combat skills. Orochimaru, even though he's a bit of a dark character, could show Naruto some really unique and forbidden jutsus that Naruto has to learn to resist the dark side of. And all this special training could make Naruto a much more formidable shinobi in the fanfic.
One idea could be a story about a young hero who discovers they have a special connection to the Dragon King. They embark on a journey to learn more about this connection and in the process, they face various challenges like battling dark forces that oppose the Dragon King's reign.