One possibility could be the power to control time. In fanfiction, this could be used in various ways, like going back to prevent tragedies or to gain more time to train. It would give Naruto a huge advantage in battles and in his quest to protect the village.
Naruto would adapt to Obito's Sharingan by relying on his strong will and his existing combat experience. He's faced many challenges before, and this would be just another one. He'd probably train with Kakashi or Sasuke to understand the Sharingan better. Since he has such a large amount of chakra, he might be able to use the Sharingan's power more frequently than others. He would also try to incorporate it into his existing fighting style, for example, using it to enhance his Rasengan or his taijutsu.
If Naruto gets Madara's power in fanfiction, he would become extremely powerful. His already impressive combat skills would be enhanced to a whole new level. He could use Madara's Sharingan abilities, which would give him an edge in predicting his opponents' moves. Also, Naruto might be able to access Madara's unique jutsu, like the Susanoo. This would make him a nearly unbeatable force in the Naruto universe of the fanfiction, and it could potentially change the entire power dynamic among the characters.
Maybe Orochimaru. Despite being a villain in the past, he is a master of forbidden jutsus and experiments. He could see Naruto as an interesting subject and give him a new arm with some dark powers, which Naruto would then have to learn to control for the greater good.
In the fanfiction, Naruto's new sensei could be a mysterious figure who has ties to the Sage of Six Paths. This person might have been waiting for the right time to appear and train Naruto. They could possess knowledge about the origin of chakra and how to fully unlock Naruto's power. It could also be someone who was once an enemy but has now changed their ways and wants to use their skills to train Naruto for the greater good of the ninja world.
He could have a 'Solar Sage Mode'. In this form, his body would be surrounded by a bright, sun - like aura. His physical abilities such as strength, speed, and agility would be enhanced to an extreme level. His attacks would also carry the power of the sun, like solar - powered punches or kicks that could cause massive damage.
Sakura is another character that can be popular in 'naruto new power fanfiction'. She might be given enhanced medical ninjutsu abilities, or even some combat - related powers that were not as prominent in the original series. For example, she could have the power to heal fatal wounds instantly or use her chakra to create powerful force fields.
It also depends on how well Naruto can control Kyoka Suigetsu. If he can master it completely, his power level could skyrocket. However, if he struggles with it, it might not be as much of an increase. There could be a learning curve where he initially has trouble using it effectively, and during that time, his power level might not show a huge jump. But as he gets more experience with the sword, his power would grow steadily, making him a force to be reckoned with not just in physical combat but also in the mental battle of illusions.
Well, perhaps the new arm comes from some kind of ancient and mysterious source. It could be an arm that was once part of a powerful ninja from the past. This new arm could have a mind of its own, at first causing Naruto some trouble as he tries to control it, but eventually they work in harmony and it gives Naruto an edge in battles against tough enemies.
In this fanfiction, Naruto might learn new and unique jutsus. His new sensei could have a different teaching style, perhaps more strict or more creative, which would greatly impact Naruto's growth as a ninja.