A really interesting plot might be that Kurama decides he wants to experience the human world more like Naruto does. So Naruto takes him on a 'tour' of the Hidden Leaf Village, showing him all the things he loves about it. But during this time, they notice some strange things going on in the village that seem to be related to an old enemy of Kurama's. They then have to use their partnership to figure out what's going on and stop it before it's too late. This could involve them using their unique bond to communicate with the villagers in a new way and uncover secrets that have been hidden for years.
One interesting plot twist could be Kurama suddenly losing his power. In the fanfic, this might force Naruto to find a new way to fight, relying more on his own ninja skills and the relationships he has built with his friends. Another could be Kurama being controlled by an unknown enemy, and Naruto has to find a way to break the control without harming Kurama. It changes their dynamic from partners to Naruto being the rescuer.
A plot could involve Naruto and the Kyuubi being separated by an evil force that wants to control the Kyuubi. Naruto then has to fight his way through various obstacles and enemies to reunite with the Kyuubi and restore their partnership.
A plot could involve Naruto having to go on a journey within his own mind to save Kurama from some sort of dark influence. During this journey, they discover hidden aspects of each other's personalities. Naruto might find out that Kurama has a soft side that he's never shown before, and Kurama could learn about Naruto's insecurities. This could lead to a stronger bond between them, and when they return to the real world, their combined strength is even greater. And as their relationship deepens, they face challenges from the outside world that test their new - found connection.
Well, a cool plot in this kind of fanfiction could be that the fusion allows Naruto to enter a new dimension or realm. In this place, he can communicate with past Hokages in a more profound way, getting their wisdom and also learning new ways to use his fused power. Maybe he discovers that the fusion gives him the ability to heal the land that has been damaged by previous battles. This would make him not just a fighter, but also a healer for the ninja world.
One idea could be that the Kurama brothers have a secret mission to protect Naruto from an ancient evil that only they know about. They use their unique powers and knowledge to train Naruto in ways that no one else can.
Perhaps in the fanfiction, the female Kurama forms a special bond with Naruto where she can transfer some of her unique powers to him in a different way than in the original story. This could lead to Naruto developing new jutsu and facing new enemies that are attracted by this new power. For example, a group of rogue ninjas who want to steal this power-transferring ability.
One idea could be that Naruto and Kurama have a day - out in the Hidden Leaf Village. They visit all the places Naruto used to go as a kid, like Ichiraku Ramen, and Kurama makes funny comments about human food. Another could be that they team up to prank the other villagers in a harmless way, just for fun.
One idea could be that Yakumo Kurama's unique powers somehow become linked to Naruto's Nine - Tails chakra, creating a new and powerful combination. They could then face a common enemy together that neither could defeat alone.
One possible plot could be that Naruto, from an early age, manages to communicate and understand Kurama's pain. Instead of the usual animosity, they quickly form a bond. Naruto could start training with Kurama's chakra earlier, leading to him being much stronger in the early parts of the story. This might change how he interacts with his peers and enemies, as he has a powerful ally right from the start.
One plot idea could be Naruto and male Kurama having to team up to face a new and powerful enemy that neither could defeat alone. They start to understand each other's powers and personalities better during the battle. Another could be Kurama teaching Naruto a new and unique form of chakra control that is exclusive to the nine - tailed fox. Or perhaps they go on a journey to discover the origin of Kurama's power and along the way, they form a deeper bond as friends.