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.
In a Juubi Naruto Attack on Titan fanfiction, Naruto could form an alliance with Eren. Naruto's ability to sense danger and his superhuman strength would be a great asset. He could teach Eren some of his ninja techniques, like how to better control his Titan form. Maybe Naruto could even find a way to use his Sage Mode to understand the Titans better.
The fanfiction could change the Naruto universe by introducing new threats. With Naruto so powerful, there could be forces that emerge to try and counterbalance his strength. Also, the story could explore different ways of using chakra, as Naruto's merged state might have unique chakra abilities. It could also affect the way ninjas are trained, as they might try to achieve a similar level of power.
First, come up with a unique concept for your alternate universe. It could be something like a world where ninjas use modern technology. Then, think about how the characters will be different. For Naruto, maybe he's not an orphan or he has different abilities. Next, plan out the plot. You can start with a small change in the Naruto universe and build on it. For instance, if the Uchiha clan was never massacred, how would that change the relationships and the overall story?
Well, it could work by having the different power systems interact. For instance, the chakra in Naruto's world and the gem magic in Steven Universe. The Juubi's power is so immense that it could disrupt the balance in the Steven Universe. Naruto, being a powerful ninja, could teach the characters in Steven Universe about combat techniques that are different from their own. And the gems could introduce Naruto and his friends to new forms of energy manipulation.
One great 'alternate universe naruto fanfiction' is 'Road to Ninja: Naruto the Movie - Another Side'. It presents a very different Naruto world where characters have different personalities and roles. For example, Naruto has a family in this AU which changes his whole dynamic.
He could fit in as a super - powerful outsider. His Juubi powers would make him stand out, but his Naruto - like personality of being friendly and determined would help him make friends. He might use his powers to help the school during times of crisis, just like he did in his own world.
One idea could be a crossover where Naruto's world is invaded by the Gem Homeworld from Steven Universe, and the Juubi's power somehow gets involved in the conflict. For example, Naruto and his friends might have to team up with Steven and the Crystal Gems to fight off the combined threats.
The Juubi could save Naruto by sharing its knowledge. In the fanfiction, the Juubi might be an ancient and wise being. It could communicate with Naruto on a spiritual level and give him insights or techniques that help him out of a tough situation. For instance, it could show Naruto a new way to use his existing jutsu more effectively, or it could reveal a secret about the enemy that Naruto is facing, allowing him to strategize better and ultimately be saved from defeat.