I would recommend 'Naruto and Shukaku: A New Alliance'. In this fanfiction, it focuses on a scenario where Naruto and Shukaku have to team up against a new, powerful enemy. It has a lot of action scenes and also some really interesting character development for both of them.
The other Jinchuurikis could be potential allies. They understand the struggles and the power that comes with having a tailed beast inside them. For example, Killer Bee, who has a good relationship with his tailed beast, could share his insights on how to better co - exist with Shukaku. Tsunade might also be an ally, as she is a powerful Hokage who could offer protection and resources to the Jinchuuriki.
Good fanfiction in this regard also pays attention to the lore of the Naruto universe. It should be consistent with the rules about chakra, jinchuriki, and the world - building already established in the original series. If it just ignores all these elements, it won't feel like a proper 'naruto and shukaku' story.
Obviously Naruto would be the main character. Shukaku itself or a representation of Shukaku's spirit could be there. Also, characters like Iruka sensei would still be around. His friends like Sasuke and Sakura would play important roles as they react to Naruto's new situation.
Well, it could be about Naruto having the powers of Shukaku in addition to his own. Maybe he has to learn to control this new power source and face new enemies who are after his unique abilities.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own (AO3). These platforms have a wide range of Naruto - related fanfictions, including those about Shukaku.
One interesting Naruto Shukaku fanfiction could be about Shukaku's backstory before being sealed into Gaara. It might explore how it lived in the desert and its interactions with other beings there.
One idea could be exploring the relationship between the Jinchuuriki and Shukaku in more depth. Maybe the Jinchuuriki tries to communicate with Shukaku in a different way than in the original series, leading to new powers or understandings. Another plot could involve the Jinchuuriki being targeted by a new group who wants to use Shukaku's power for their own evil purposes. The Jinchuuriki then has to fight not only to protect themselves but also to keep Shukaku from being misused.
There could be a powerful and jealous ninja from another village. This ninja wants the power of the Shukaku for himself. He sees the relationship between Naruto and the female Shukaku as an obstacle to his goal, so he devises plans to separate them and capture the female Shukaku, making him a major antagonist in the fanfiction.
Their relationship could start with mistrust. Since Shukaku is a tailed beast, Naruto might be cautious. But as they interact more, like when they are forced to fight together against a common foe, they start to respect each other.