Well, perhaps in the fanfic, Naruto has to team up with his friends in a unique way to seal the Juubi. For example, Sasuke could use his Sharingan to help Naruto locate the weak points of the Juubi while Naruto does the actual sealing. And Sakura could use her medical ninjutsu to keep Naruto in top shape during the process.
Sasuke is likely to be an important character. His power and his relationship with Naruto could play a big part in the story. He might help Naruto in the fight against the Juubi or have some other role related to the sealing process.
The idea of Naruto sealing the Juubi is quite common in Naruto fanfictions. If Kurotsuchi is involved, it could be that the author wants to explore a different kind of relationship. For example, Kurotsuchi could be from a different village and her interaction with Naruto during this momentous event could lead to a new alliance or at least a better understanding between their respective villages. Also, the sealing of the Juubi by Naruto is no easy feat. It would require a great deal of chakra control and knowledge of sealing jutsus. Kurotsuchi, with her own skills in earth - based techniques, might be able to contribute in unexpected ways, like creating a stable environment for the sealing to take place.
Well, one possibility could be that Naruto's sealing of the Juubi is a turning point in the story. Mei might play a role in helping Naruto deal with the after - effects of such a powerful sealing. Maybe she uses her unique water - based abilities to create a protective barrier around the sealing site to prevent any leakage of the Juubi's chakra. It could also lead to a new alliance between their respective villages, with both Naruto and Mei as the main proponents of this newfound friendship.
In some versions of fanfiction, Naruto might use a new and powerful sealing jutsu that he has either created or learned specifically for this purpose. It could be a jutsu that combines his Uzumaki heritage's sealing knowledge with his own unique chakra control.
One possible plot development could be that the village is in great danger from an enemy too powerful to defeat directly. Naruto, seeing no other way, seals himself away to act as a last - line - of - defense deterrent. If the enemy tries to completely destroy the village, Naruto's sealed power could be unleashed to counter them.
It could be a new and extremely powerful ninja from a far - off land who has a vendetta against Konoha. His power might be so great that Naruto decides the only way to stop him in the long run is to seal himself away as a sort of trap for when the antagonist gets too close to achieving his goals.
One consequence could be that Naruto has a constant struggle to keep Kaguya's power in check. He might experience internal battles within his mind as Kaguya tries to break free.
Mei might start as a relatively minor character in the fanfiction. But as she gets involved in Naruto's mission to seal the Juubi, her character could grow. She could become more confident in her abilities and start to take on more leadership roles. For example, she might lead a group of ninjas to protect Naruto while he is performing the sealing. This experience could make her more respected in her own village and also in the wider ninja world.