One plot idea could be that the female Juubi has a unique connection with Naruto's chakra. Maybe she is a misunderstood being and Naruto, with his ability to see the good in others, tries to befriend her. This could lead to them teaming up against a common enemy who wants to use the Juubi's power for evil.
One plot idea could be that the Female Kyuubi has to team up with Juubi Naruto to fight a common enemy. Maybe an ancient evil that threatens the entire ninja world. They start off distrusting each other but as they face challenges together, they learn to work in harmony.
In this fanfiction, perhaps Naruto has a pre - destined connection to the Juubi. It could be that in a past life he was related to the origin of the Juubi, and this connection starts to resurface during his adventures, leading to a whole new set of challenges and powers for him.
Another plot could be a story where Naruto is somehow lost in Moka's world. He has to adapt to the new rules and customs while also trying to find a way back home. Along the way, he befriends Moka and they learn from each other's strengths. For example, Naruto teaches Moka about the importance of friendship and loyalty in his ninja world, and Moka shows Naruto how to use his chakra in new and unexpected ways in her world.
One idea could be a male character who has a unique bond with the Juubi. Maybe he's able to communicate with it on a deeper level than others. He could use this connection to gain new powers and face off against powerful enemies in the Naruto universe. Another plot could involve the male character trying to tame the Juubi's wild nature and use its energy for good, like protecting the Hidden Villages from a new, greater threat.
One idea could be a crossover where the Juubi's power somehow gets transferred to a character in Soul Eater and they have to learn to control it. Another could be Naruto getting lost in the Soul Eater world and having to adapt to their way of fighting and dealing with souls.
In the 'naruto juubi alternate universe fanfiction', it would be interesting if the characters' relationships were reversed. Like Sasuke could be the one trying to protect Naruto who has the Juubi's power, because he realizes that Naruto's power is the key to a new world order that could benefit all ninjas.
One possible plot idea could be a crossover where characters from Naruto and Legend of Korra have to team up to face the Juubi. Maybe the Avatar from Legend of Korra discovers a new power that is linked to the chakra of the Juubi in the Naruto world.
A cool plot might be that a mysterious figure uses the concept of a harem to manipulate Naruto in the context of the Juubi. The harem members could be from different villages and have different abilities related to the Juubi's energy. Naruto has to figure out who is behind this manipulation while also dealing with his growing feelings for the members of the harem. He could discover that there is a deeper connection between the Juubi and the creation of this harem situation, and that by solving this mystery, he can prevent a greater disaster.
A really exciting plot could involve Naruto getting trapped in a time - loop within the Juubi dimension. Every time he tries to find a way out, he ends up back at the starting point. He has to figure out how to break the loop by solving a mystery related to the Juubi's power. This would require him to interact with different versions of characters he knows, who may have different personalities and motives in this strange dimension.
One possible plot idea could be that the female Kyuubi and female Juubi are initially seen as threats by the Hidden Leaf Village. Naruto, being the protagonist, decides to approach them differently. He tries to understand their motives and discovers that they have been misjudged. The female Kyuubi might have a past connection to Naruto's family, and the female Juubi could hold the key to a great power that can save the ninja world from a new, emerging evil. Naruto then teams up with them, facing opposition from within the village but ultimately proving that they can be allies.