One interesting plot could be that Naruto, as a sage, sacrifices himself to seal away a powerful ancient evil. His death then becomes a catalyst for a new era of peace as his friends vow to carry on his legacy. This could lead to his friends developing new powers in his memory.
Well, in some fanfictions, Naruto might die in a fight against a new, extremely powerful enemy that he underestimated. This enemy could have a unique ability that nullifies Naruto's powers. For example, if the enemy can absorb all forms of chakra, Naruto would be at a severe disadvantage. His death could then lead to a great upheaval in the ninja world, with his friends and comrades vowing to avenge him.
One interesting plot could be Naruto exploring new and unique sage training methods that are not in the original story. For example, he might discover a hidden sage realm with different rules and challenges.
In certain 'naruto sage training fanfic', there could be a plot where Naruto's sage training is intertwined with a prophecy. He has to train in a specific way to fulfill the prophecy and save the ninja world. This could lead to him having to master skills and powers that are far beyond what he originally thought possible during his sage training journey.
One interesting plot could be Naruto faking his death to go undercover and expose a hidden conspiracy within the ninja world. He might change his appearance completely and work his way into the enemy's ranks secretly.
One interesting Naruto sage fanfiction could be about Naruto exploring new sage abilities that were not shown in the original series. For example, he might discover a way to combine sage mode with his other jutsu in a more powerful and unique way.
One idea could be that Naruto has to go through a series of ancient trials in a hidden and dangerous realm to become a sage. He might face illusions of his past failures and have to overcome them. Another could be that he has to learn from a reclusive and cranky old sage who initially doesn't trust him but Naruto wins him over with his determination. And a third could be that Naruto discovers a new form of chakra related to sage mode that he has to master while also fending off enemies who want to steal this power for themselves.
One possible plot could be Naruto learning unique jutsu directly from the Sandaime. For example, he might be taught some long - forgotten sealing techniques that give him an edge in battles. Another plot could involve Naruto getting insights into the village's history and politics from the Sandaime, which helps him better understand his role in the village.
One interesting plot could be the daughter inheriting Naruto's determination and Sakura's medical skills. She might go on a journey to find a cure for a new, mysterious illness that's plaguing the village. Along the way, she meets new friends and overcomes various challenges using her unique combination of skills.
One interesting plot could be the discovery of Kakashi's father's hidden jutsu that he passed down secretly. Maybe Naruto stumbles upon an old scroll related to it during one of his adventures. Another could be a story where Kakashi's father returns as a spirit to guide Kakashi in a difficult situation and Naruto gets to witness this special bond.
Maybe a story where they have a falling out over a misunderstanding. Shikamaru thinks Naruto is being reckless and endangering the village, while Naruto feels Shikamaru doesn't trust him enough. But then they come to realize their friendship is stronger than this small bump and they make up. This could show the depth of their relationship and how they can overcome differences.