Regarding Kakashi, he would be both proud and a bit worried. Proud because Naruto has grown so much, but worried about how Naruto will handle such great power. Kakashi would offer more guidance and training, and their relationship would shift from mainly teacher - student to more of a partnership, with Kakashi acting as an advisor to Naruto on how to use his powers for the greater good.
His relationship with Sasuke would likely become more complex. Sasuke might be both jealous and intrigued by Naruto's new powers. Naruto would have to prove that he still values their friendship despite his increased strength. With Sakura, she might see Naruto in a new light, perhaps with a bit more admiration as he now has such rare and powerful abilities.
It changes the story a great deal. First, the Mokuton gives him an edge in combat as he can manipulate plants and wood. This could be used in creative ways like creating huge forests to trap enemies or using wooden constructs for offense. The Rinnegan, on the other hand, is a whole new level of power. He could potentially use it to travel between dimensions, which would open up new plotlines. For example, he could discover new threats or allies in other dimensions. Overall, his character would become more complex as he tries to master these new powers.
Well, relationships in Naruto Mangekyou Sharingan and Rinnegan fanfiction are often re - defined. When a character unlocks the power of these eyes, their friends may feel a sense of duty to protect them from those who would seek to harm them for their power. However, enemies may target the character's loved ones to get to them. Also, in some fanfictions, characters with these eyes may form a special bond with others who have a similar power or a connection to the origin of these eyes. This can create new alliances and rivalries within the Naruto universe.
His relationship with Sasuke would likely be very different. Since Sasuke has also had experiences with the Rinnegan, they might now have a new level of understanding between them. They could train together to master the powers of the Rinnegan or compare notes on how to use its abilities.
A fanfiction could center around a battle between two powerful ninjas, one who has mastered the Mokuton and Sharingan, and the other who has the Rinnegan. The fight could be not just about physical combat but also about the clash of different ideologies related to these powers. The one with the Mokuton and Sharingan might believe in a more traditional view of power, while the Rinnegan user could have a more radical view.
One possible main antagonist could be a rogue ninja who also has a connection to the Mokuton or Rinnegan powers. Maybe he was once part of a secret experiment that went wrong and now he wants to take Naruto's powers for himself. Another option could be an ancient being that was sealed away long ago and is now awakened by Naruto's new powers. This being could see Naruto as a threat to its plans of world domination.
With Kakashi, Naruto's relationship would also shift. Kakashi has had experience with the Sharingan and knows about powerful dojutsu. He would be both amazed and a bit worried about Naruto having the Rinnegan. He might try to mentor Naruto more intensively to make sure he uses it for good and doesn't let the power corrupt him. Naruto would look up to Kakashi even more as he tries to learn about his new power from Kakashi's knowledge.
If Naruto had both powers, his relationship with Sasuke would be affected. Sasuke might see Naruto as an even greater rival or, on the other hand, might be more willing to work with him. They could train together to better understand and control these new combined powers. Sakura might be in awe of Naruto's new abilities and try to support him in a different way, perhaps by researching more about the Sharingan and Rinnegan to help him. Kakashi, having knowledge of the Sharingan, could mentor Naruto in using it in combination with the Rinnegan.
His relationship with Sasuke would likely be very different. Since they both now have extremely powerful eye - related abilities, they might have a new kind of rivalry or, on the contrary, a deeper understanding. They could train together to master their powers and protect the village.
In the wider ninja world, his relationship with other villages would change. Some villages might see him as an even greater threat now that he has the Rinnegan, and might try to form alliances against him. However, Naruto being Naruto, he would use his new power to show that he still has the same kind - hearted goals. He would try to use the Rinnegan to bring about peace even more strongly, and over time, win over those who were initially suspicious.