In terms of his relationship with Kurapika, it would be very tense. Kurapika is on a vendetta against the Phantom Troupe, and Killua joining them would put him in direct opposition to Kurapika. Killua would have to deal with Kurapika's hatred towards the troupe while also trying to keep his true intentions hidden. And with the troupe members, his relationships would be a mix of fear, respect, and secrecy as he tries to navigate the dangerous world of the Phantom Troupe while still holding onto his own values.
For Gon, his relationship with Chrollo would be crucial. Chrollo is the leader of the Phantom Troupe, and Gon's sense of justice might clash with Chrollo's leadership. However, Gon might also see some good in Chrollo and try to influence him in a positive way. Killua would likely form alliances with the more practical members of the troupe, like Pakunoda. She's smart and has a good understanding of the group's dynamics. Killua could learn a lot from her about how to survive within the troupe. As time passes, both Gon and Killua would have to adapt to the different personalities and values of the Phantom Troupe members, which would be a continuous process of give - and - take.
One possible plot could be that Killua joins the Phantom Troupe in order to protect Gon. He might think that by infiltrating the troupe, he can keep Gon safe from their potential threats. Maybe he initially pretends to be on their side, but as time goes on, he starts to question his own actions and the morality of the troupe.
Naruto's relationship with his sensei, Kakashi, would be severely strained. Kakashi has always been a guiding figure for Naruto, and Naruto joining the Akatsuki would seem like a betrayal. However, Kakashi might also suspect that Naruto has an ulterior motive. As for his relationships with the other Konoha ninjas, they would be filled with suspicion and mistrust. But Naruto could also form new relationships within the Akatsuki. He might befriend some of the members who have a bit of good in them, like Konan perhaps, and together they could work towards a new future for the Akatsuki.
They might bring a new perspective to the Phantom Troupe. Gon's unwavering sense of justice could influence some members to question their own actions. Killua's knowledge of the underworld outside of the troupe's usual scope could also be valuable. Maybe they would start to take on different types of jobs, not just the typical heists and assassinations. For instance, they could get involved in helping people who are being oppressed by other criminal organizations, which would be a radical change for the Phantom Troupe. But this new direction could also divide the troupe into those who support Gon and Killua's ideas and those who oppose them.
His relationship with Sasuke would be severely affected. If Naruto is betrayed by Konoha and joins Kumo, Sasuke might see it as a sign of weakness or a wrong decision. Their rivalry could turn into something more complex, with Sasuke perhaps trying to bring Naruto back to Konoha or seeing him as an enemy. With his friends in Konoha like Sakura, there would be a lot of heartache. They might not understand his decision at first, but over time, some might come to realize the reasons behind it.
Naruto's relationships would shift significantly. In Kirigakure, he'd have to form new friendships with local ninjas. These relationships would be based on different foundations compared to his Konoha friends. He might find it hard to trust at first. And his relationship with Kakashi would also change. Kakashi would probably be concerned about Naruto's new situation but also respect his decision to some extent. Naruto would have to start from scratch in building trust and camaraderie in Kirigakure.
With his family - like figures in Konoha, such as Iruka, the relationship would be put to the test. Iruka would probably be heartbroken but also hope that Naruto is doing what he thinks is right. In Iwa, Naruto might find a new mentor - like figure who could teach him different things compared to what he learned in Konoha. This new relationship could shape his ninja path in a whole new way.
His relationship with Alfred would be severely strained. Alfred has always been Batman's moral compass and a source of support. If Batman joined the Dark Side, Alfred would be heartbroken and would try his best to bring Batman back to the light. There would likely be many arguments between them as Alfred tries to remind Batman of his true values.
Well, think about it. Harry's relationship with his friends is ruined. Hermione might try to convince him to come back to the good side, but Harry, feeling so betrayed by his past experiences, would resist. With Voldemort, Harry would be in a very strange position. Voldemort doesn't really trust anyone, but he would use Harry to his advantage. Harry, in turn, might start to see Voldemort as a sort of father figure, which is a very warped view considering Voldemort's nature. And the wizarding world as a whole would view Harry as a fallen hero, and there would be a lot of fear and hatred towards him.
His relationship with Sasuke would become more complex. Since they are from different villages now, there would be a new dynamic. Sasuke might see Naruto's move as a betrayal to Konoha at first. But Naruto's intention could be to bridge the gap between the two villages for Sasuke's sake too.