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.
A more complex plot could involve a time - traveling aspect. The Juubi Naruto from the future travels back in time to Moka's world. He knows that an event in the future is linked to something that is about to happen in Moka's world. So, he has to prevent this event from occurring. This would involve a lot of mystery, as Naruto has to figure out the connection between the two worlds and the events while also dealing with the various characters in Moka's world, some of whom may be initially suspicious of him.
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.
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.
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.
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.
One idea could be that Naruto, with his kitsune powers, and Moka end up in a parallel dimension where they have to work together to find a way back home. They face strange creatures and have to learn about each other's abilities along the way.
Maybe Inner Moka has to go to the Naruto world for some reason, like to find a rare ingredient for a potion that only exists there. Naruto helps her navigate his world and in the process, they learn about each other's cultures and powers. Along the way, they also have to face some of Naruto's enemies who are interested in Inner Moka's vampire abilities.
Maybe there's a story where an ancient evil is threatening all of their worlds. Naruto, Moka and Kurumu are chosen as the representatives to fight against it. At first, they have trouble working together due to their different personalities and ways of doing things. But as they face more and more difficult battles against the evil, they start to understand and trust each other more, and eventually combine their powers to defeat the great threat.