The mask could be central by being the source of a mystery. Everyone in the fanfiction is trying to figure out what it is and what it can do.
Well, it could be the key to saving the ninja world. Maybe it has some sort of power that can stop an upcoming great evil. So, all the characters are either trying to protect it or steal it depending on their motives. This would make it the central element as the whole story would revolve around its fate.
The vest could be central by being a symbol of power. For example, in a story, the main character could be a young and inexperienced ninja who is given a Jounin vest as a sign of great trust. This then becomes a source of motivation for the character to live up to the expectations associated with the vest.
One idea could be a story where Obito's mask holds a hidden power. For example, it could be a key to an ancient jutsu that was sealed away long ago. Another plot could involve a character trying to steal the mask for its significance in the ninja world.
It could be the center of a power struggle. Different ninja groups or characters might want the Raijin Sword for themselves. Some may want it for its power, while others may want to keep it out of the wrong hands. This can create a lot of conflict and drama in the fanfic. The main character could be caught in the middle of this struggle, either trying to protect the sword or having to decide who is worthy of wielding it.
Obito's influence would likely make Naruto more aware of the darker side of the ninja world. Naruto is usually very optimistic, but with Obito's guidance, he would see the hardships and betrayals that can happen. For example, Naruto might become more cautious in his trust of others.
The story could start with Naruto finding Obito in a desolate place. Naruto would be curious and approach him. Then, they would exchange words, and Naruto would offer his help to Obito. As they interact more, they might face some small - scale battles together against rogue ninjas or other threats. This would build trust between them.
To develop Naruto in a crossover with Obito, you can put him in situations where he has to use his wits against Obito's Sharingan - related abilities. This would force him to become more strategic. Also, Naruto could learn about the Uchiha clan's history from Obito, which would expand his knowledge. As for Obito, Naruto's presence could make him confront the fact that his actions have consequences. He could start to see the value in the bonds that Naruto has with his friends and village, and this could lead to a change in his goals and values.
In this fanfiction, Obito's development can be quite interesting. He may begin with his own motives that are not entirely pure. However, as he spends more time with Naruto, he starts to see the world through Naruto's eyes. This could lead to him becoming more empathetic towards others in the ninja world. For example, he might start to understand the importance of protecting the village and its people, just like Naruto does.
It might give Naruto new types of jutsus. For example, if the Kitsune have the ability to create illusions, the mask could grant Naruto the power to use more advanced genjutsu. He could use these illusions not only in battle but also to deceive his enemies in strategic ways outside of combat.
One possible fanfiction could be about Naruto and Obito teaming up to face a new, powerful enemy. They could combine their unique skills, like Naruto's Rasengan and Obito's Kamui. Their relationship could start off rocky due to their past differences but gradually turn into a strong bond as they fight side by side.
A fanfiction story could start with Naruto being in a desperate situation where he feels that the normal path to peace is not working. So, he decides to team up with Obito and Madara. At first, they seem to be working towards a common goal. But then, Naruto realizes that their means are too extreme. For example, he discovers that the Infinite Tsukuyomi they plan would take away people's free will. He then has to find a way to stop them while still maintaining some sort of alliance. This could lead to a complex web of relationships and power struggles within the group.