Sakura should be in it. She can provide medical support when Naruto is in trouble due to the One Tail's power. And Sasuke too. His rivalry with Naruto can add an interesting dynamic. Maybe he could be initially skeptical about Naruto's ability to control the One Tail, but later comes to respect his growth.
Obviously Naruto himself. He is the main character and his connection to the One Tail is the core of the story. Kakashi would also be a great addition. His wisdom and experience can help Naruto deal with the challenges related to the One Tail, like teaching him new ways to control it.
Definitely Naruto himself, since it's a drunk Naruto fanfiction. His friends like Sasuke and Sakura should be included too. Sasuke could react in his typical stoic but secretly concerned way when Naruto is drunk. Sakura could be the one trying to get Naruto to sober up or at least stop making a fool of himself. Kakashi would also be great, as he could have some humorous reactions to Naruto's drunken antics.
Natsu could be a great addition. His brash and powerful nature could contrast with Ren and Sherry's more calculated and magical - knowledge - based approaches. He could join them on a mission and provide the muscle when they encounter tough opponents. Also, Lucy would be good as she has a wide range of celestial spirits that could be useful in different situations. Her kind and curious personality would also add an interesting dynamic to the group.
For a more unique take, including Jiraiya could be great. His pervy but knowledgeable personality could lead to some humorous and yet useful moments. He might have some ancient knowledge about the connection between the Naruto world and the Pokémon world where Darkrai comes from. On the Pokémon side, Cynthia could be a great addition. As one of the strongest Pokémon trainers, she could offer a different perspective on Darkrai and also help in battles against any enemies that might be using Darkrai's power for evil.
Haku should definitely be included. Since Haku was Zabuza's loyal follower, his presence can add depth to the story. He could act as a mediator between Naruto and Zabuza at times. Also, Kakashi can be a great addition. His history with Zabuza makes for an interesting dynamic, and his mentoring of Naruto can play a role in how Naruto interacts with Zabuza.
Well, in addition to Naruto and Urahara, Ichigo from Bleach could be a great addition. Since Urahara has a connection with Ichigo, and Naruto's energetic and positive nature could create an interesting dynamic with Ichigo's more brooding personality.
Kakashi could be a good character to put in. His experience and wide range of ninjutsu could be useful in the story. For Thalia's side, Luke could be included. His conflicted nature and his skills would add a layer of intrigue, especially when interacting with Naruto and Thalia, as they try to figure out whether to trust him or not.
Definitely Naruto himself. His determination and positive attitude can bring a lot to the story. Lala too, of course, with her fun - loving and inventive nature. Sakura could also be a great addition. She could interact with Lala in interesting ways, perhaps learning about Lala's technology and applying some of her medical skills to help Lala if she gets injured.
Madara Uchiha would be an excellent character to include. His long - standing relationship with Hashirama, filled with both friendship and enmity, and his connection to Sasuke and the overall ninja world's history would make for a very engaging fanfiction.
Naruto himself is a must - he's the main character after all. Sasuke could also be great as his rival. Their interactions around the kit would be interesting, like if they both wanted it for different reasons. Sakura could be included too, maybe she helps Naruto figure out how to use the kit.
Definitely Sasuke. His complex relationship with Naruto provides a lot of material for fanfiction. You can explore their friendship, rivalry, and how they grow together. Kakashi is also a great character to include. His wisdom and unique jutsu can add depth to the story. And of course, Sakura. Her growth as a kunoichi and her relationships with Naruto and Sasuke can be interesting to write about.