Sasuke's reaction could be complex. He might see Naruto as a more powerful opponent or ally, depending on their current relationship in the fanfiction. If they were still rivals, Sasuke might be intrigued by Naruto's new form and want to test his own strength against it. If they were friends, Sasuke would be concerned about Naruto's ability to control himself and would offer his help in any way he could.
His relationship with Hinata might be affected. She might be a bit more worried about him at first, but also see him as even more of a hero for having to endure this new transformation. With his friends like Shikamaru and Choji, they might be more cautious around him initially, but still be there to support him. They would have to get used to his new state and the potential danger it could bring.
His relationships with his friends would become more complex. His friends might be a bit scared or at least unsure about this new side of him. For example, Sakura might be worried about how to approach him now. Sasuke, on the other hand, might see Naruto in a completely different light, either as a threat or as an even more interesting rival. His relationship with the village elders would also be different. They might try to keep a closer eye on him or even isolate him to some extent.
In terms of his relationship with the other tailed beast hosts, it could become more complex. He might have a new understanding of what they've been through, but at the same time, they could be jealous of his new form. Some might see him as an upstart, while others might look to him for leadership. Naruto would have to navigate these tricky relationships carefully, all while trying to figure out his own new identity as a tailed beast.
He might become more wild and instinctive. Tailed beasts are known for their raw power and basic instincts. So Naruto could be more impulsive, acting on his first thoughts rather than thinking things through. For example, in a fight, he might not hold back as much as he usually does as a normal ninja.
One possibility is that Naruto would initially be confused and struggle to control his new form. He might accidentally cause destruction in the village as he tries to figure out his new powers. But with the help of his friends, like Sasuke and Sakura, he could start to learn to harness the tailed beast's abilities for good, perhaps even developing new jutsu.
Naruto's relationship with the other villages would be transformed. Some villages might be afraid that he would use the power of all tailed beasts against them. However, villages like Iwagakure, which had a history of conflict with Konoha, could now see Naruto as a unifying force. The younger generation in all villages would probably idolize him more than ever, seeing him as a symbol of ultimate power and justice.
Her relationship with her father would be different. She would no longer be the naive girl he once knew. She could be more of an equal to him, advising him on political matters. For example, she could tell him not to trust Littlefinger as much. And with her sister Arya, she might be more open and understanding from the start, instead of having the initial rifts between them.
His relationships with his friends would become more complex. For example, Sasuke might be jealous or in awe of Naruto's new power. Sakura might see him as more of a distant figure, someone she can't fully understand anymore. And his old teachers like Kakashi would be in a position of having to respect Naruto's new status while still trying to guide him in some ways.
Naruto's relationships would experience a significant shift. With Sarutobi as his guardian, he would have a closer relationship with the Anbu. He would be more involved in the inner workings of the village at an earlier stage. His relationship with Kakashi would also be different. Instead of Kakashi being his main mentor, Sarutobi would play that role. This would mean that Naruto would approach his training and missions with a different mindset, which in turn would affect how he relates to his comrades and opponents.
His relationships with his friends in Konoha would become more complicated. They might be suspicious of Medusa and worry about Naruto being influenced by her. But at the same time, Naruto could try to convince them that Medusa is not all bad. With his enemies, they might be more afraid of him because of his connection to Medusa.
If Naruto was raised by Orochimaru in fanfiction, his relationships would be turned upside down. His friendships from the Leaf Village would be in jeopardy. Since Orochimaru is not one to value the kind of loyalty and friendship that Naruto's friends in the Leaf do, Naruto would have a hard time understanding and maintaining those relationships. He might even be hostile towards them, seeing them as obstacles in his pursuit of power. His relationship with the Hokage would also be a mess. Instead of looking up to the Hokage as a role model, he would probably view the position as something to be conquered or undermined, following Orochimaru's ideology of power - seeking.