In some fanfictions, Orochimaru might be an ally. He has always been interested in Naruto's power and could see an opportunity in Dark Naruto. Another could be Sasuke. If Sasuke is still on his revenge path and sees Dark Naruto as a way to bring down the village, he might team up. And there are also some fan theories that some of the outcast ninja from Konoha who have grudges might side with Dark Naruto.
Well, Kabuto could be an ally. Since he was once Orochimaru's follower and is always looking for power, he might see Dark Naruto as a means to gain more influence. Tobi (Obito) could also be a likely ally. He has his own vendetta against Konoha and Dark Naruto's destruction would fit into his plans. Additionally, some of the rogue ninja who were once persecuted by Konoha for minor offenses might join Dark Naruto, feeling that Konoha has wronged them too much.
I think Hinata could be an ally. She has always been in love with Naruto and would not stand by while he is in danger from Dark Naruto. Additionally, Shikamaru is smart and strategic. He might see the threat of Dark Naruto to the village and decide to assist Naruto, using his intelligence to come up with battle plans.
Sakura and Sasuke are very likely allies. Sakura has her medical skills and combat abilities, and Sasuke, despite his past issues, has great power. They've been comrades with Naruto for a long time.
Well, in many such fanfictions, one main plot point could be the reason behind Dark Naruto's turn against Konoha. It might be due to past betrayals or the village's treatment of him. Another could be the initial acts of destruction, like targeting key buildings or shinobi. And finally, there could be a part where the remaining shinobi of Konoha try to stop him, either through force or by trying to reach the 'good' side of Naruto still inside.
Sakura would definitely be one of his allies. She's always been by Naruto's side, and in this fanfiction, she could help him with his disguises, like using her medical ninjutsu to create more realistic physical changes. Kakashi could also be an ally. His intelligence and experience would be valuable in planning Naruto's undercover missions. He could teach Naruto how to act more convincingly in different disguises.
I think Gaara could be an ally. Gaara has control over sand and is very powerful. He and Naruto have a mutual respect for each other. Additionally, Jiraiya. Jiraiya was Naruto's mentor and has a vast knowledge of different jutsu and combat techniques that could be used against Omega Shenron.
Well, first of all, Jiraiya might return in some form, like a spirit guide or something, and be an ally to Naruto. Tsunade would also be there, using her leadership and medical ninjutsu. And then there are the new generation characters like Boruto. He could learn from Naruto and help out, seeing as he also has his own unique abilities. The Allied Shinobi Forces from the previous big battles might also reunite to support Naruto in saving the world.
Sasuke would be a likely ally. They have a long - standing relationship and have fought side by side before. Sasuke's Sharingan and his own unique abilities would be a great asset against the Ten - Tails.
Sasuke is often an ally. Since Sasuke also has his own issues with the village and a thirst for power, he may see Dark Naruto as a kindred spirit. They could team up to take on the Hidden Leaf together. Another common ally could be Orochimaru. Orochimaru is always interested in power and the unique abilities that Dark Naruto might possess. He could offer his knowledge and resources to help Dark Naruto in his revenge plot.
Sakura could also be an ally. As a medic - ninja, she could help Kagome if she gets injured. And Sakura is used to dealing with strange situations and new people, so she would be open to helping Kagome.
The other shinobi villages might also be antagonists. If Naruto's village is seen as a threat because of his power, they could target him. This would make Naruto angry as he's being attacked for no good reason other than fear. Their actions against him and his village could lead him to a darker state as he has to fight back against these external threats.