If Naruto were trained by the Shinigami in a fanfic, his relationship with his friends and allies would become more complex. His new powers could make some of his friends, like Sakura, feel a bit left behind. She might strive to catch up to him in a different way. Also, Naruto's connection to the Shinigami could put a strain on his relationships with those who are more superstitious in the village. However, it could also attract new allies who are interested in the power of the Shinigami or see Naruto as a key to unlocking secrets about the afterlife.
Naruto's relationship with his sensei, like Kakashi, would change. Kakashi would be both proud and cautious. Proud because Naruto is getting stronger, but cautious as the Shinigami - related training is uncharted territory. His bond with the other villagers would also shift. Some might see him as a protector with new, otherworldly powers, while others might be suspicious of the Shinigami's influence on him. Overall, his relationships would be in a state of flux as he adapts to his new self after the training.
His relationship with his friends would likely change. He might become more distant at first as he focuses on his training with the female shinigami. But in the long run, his new powers and insights could make him a better protector of his friends. For example, he could use his newfound skills to rescue them from more dangerous situations.
His relationship with Sasuke might be affected. Naruto might approach Sasuke differently, with new strategies learned from Zetsu. He could be more secretive about his intentions towards Sasuke, which might either make Sasuke more curious or more distrustful. With his friends in Konoha, they might be a bit wary of Naruto at first because of his new training source. But once they see that Naruto is still on their side, they would support him.
His relationship with Sasuke might change. Sasuke might be more intrigued or even a bit jealous of Naruto's new power. Naruto could use the Shinigami eyes to better understand Sasuke's inner turmoil, which is often related to his own spiritual and emotional state.
If Naruto was trained by the Akatsuki in fanfiction, his relationships would be completely transformed. For starters, his relationship with Kakashi would be strained. Kakashi has always been Naruto's mentor in a way, and seeing Naruto side with the Akatsuki would be a shock. His friends like Sakura and Shikamaru would also be confused and probably try to bring him back to the 'right side'. And his relationship with the villagers of Konoha would turn sour as they would fear his new - found Akatsuki - related powers.
In this fanfic, Naruto's relationships would be in flux. Regarding his friends, they would look up to him as he gains knowledge and power from the Sannin. His relationship with Sakura could change as he becomes more capable of handling Sasuke - related issues. With the village elders, Naruto might gain more respect as they see his potential growing under the Sannin's tutelage. His connection with the Nine - Tails would also be different. As he learns from the Sannin, he could use the Nine - Tails' power in new ways, which might change how he is perceived by the fox and how he interacts with it. All in all, his relationships would be reshaped by the new experiences and skills he acquires from the three Sannin.
His friends might be a bit wary of him at first. Since the Shinigami is often associated with death, they could be a bit scared of his new powers. But over time, they would probably come to accept it and see how he uses it for good.
With Sakura, Naruto's attitude could shift. Instead of being the goofy, love - stricken Naruto she's used to, he could become more distant. He might be so focused on his training with Zabuza that he doesn't have time for Sakura's attempts to get his attention. This could make Sakura feel rejected and lead to some tension between them.
Naruto's friends might be initially suspicious of the new skills and attitude he gets from Slade's training. For example, Sasuke could see Naruto's new combat style as too ruthless and this could create tension between them. Sakura might worry that Naruto is getting too influenced by a dangerous figure. However, if Naruto can show that he's still the same person at heart, they could gradually accept his new abilities.
His combat abilities would become more diverse. Madara could teach him new forms of taijutsu and ninjutsu. For example, Naruto might learn some of Madara's signature space - time ninjutsu, which would give him an edge in battles. His chakra control would also improve as Madara is very proficient in chakra manipulation.
He might become more cautious. Tsunade is a more calculating ninja compared to some of Naruto's previous mentors. So Naruto could start to think before he leaps, rather than just charging into battle head - first all the time.