Obviously, Naruto is the central character. But there are also often other characters like Jiraiya. Since Jiraiya was Naruto's mentor in the original story and had knowledge about sage mode, he often appears in fanfics to guide Naruto in his training. Another common character could be Kakashi. He may offer some advice or support to Naruto during the training process.
Jiraiya is often a common character. Since he was Naruto's teacher and had knowledge of sage training himself, he might appear in the fanfiction to guide Naruto further. Another one could be Kakashi. He is always looking out for Naruto and could be involved in the training in some way, like providing strategic advice.
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 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.
Naruto might also try to find alternative ways to gain strength. He could explore the forest around the village to find new training areas or discover new chakra - related phenomena. He has a curious nature, and this could lead him to stumble upon something that gives him an edge in his training, like a hidden hot spring that has special chakra - enhancing properties.
In the original Naruto story, the training is more in line with the established ninja academy and traditional Sensei - student relationships. But in 'naruto training lemon fanfic', it might be more experimental. Maybe Naruto tries some unorthodox methods of training that are not seen in the original.
Training in fanfictions often makes Naruto more confident. As he masters new skills, he becomes surer of himself in battles and in his interactions with others. For example, if he learns a powerful new jutsu, he'll carry himself with more pride and authority.
Naruto might initially be very disappointed. He has always been eager to train and become stronger. So being denied by Kakashi could make him feel a bit down. But he could also be defiant. He might start training on his own, determined to show Kakashi that he doesn't need his approval to get stronger.