The Akatsuki members could be the antagonists. Since Sasori was part of the Akatsuki, other members might want the scrolls for their own evil plans. They could try to stop Naruto from getting to the scrolls.
Maybe there's a new group of villains introduced specifically for this fanfiction. They could be a group of power - hungry ninja who heard rumors about Sasori's scrolls and are determined to get them at all costs. They set up various obstacles and battles for Naruto and his friends during their search for the scrolls.
There could also be some rogue ninja clans. They might see the power that Sasori's scrolls could hold, like advanced puppet - making or some forbidden jutsu. So they become the antagonists, trying to steal the scrolls from Naruto or whoever is in possession of them.
One possible plot development could be that Naruto discovers the scrolls in an old, abandoned hideout. Maybe the hideout is full of traps set by Sasori long ago. Naruto, with his ninja skills, has to overcome these traps to reach the scrolls.
The Akatsuki could still be the main antagonists. Even though Sasori is training Naruto, the rest of the Akatsuki might view Naruto as a threat and try to eliminate him. Also, Orochimaru could be an antagonist. He might be interested in the new skills Naruto is learning from Sasori and try to steal them for his own experiments.
He might discover new types of puppets that Sasori was in the process of creating. Maybe some with unique abilities that no one has ever seen before.
In the fanfiction, they could have a mentor - mentee relationship. Naruto, with his big heart and positive attitude, could be the one to show Sasori a different way of looking at things, like a mentor. Or Sasori could teach Naruto some of his puppet - related skills, acting as a mentor in that aspect.
They could be on a journey to find a rare material for Deidara's art. Sasori, with his knowledge of the ninja world, helps guide them. Along the way, they encounter various strange creatures and ninja clans. They might have to fight off some who are after the same material.
In a fanfiction, Deidara and Sasori could be sent on a secret mission to infiltrate a hidden village. Deidara uses his clay creations to distract the guards while Sasori sneaks in with his puppets. As they progress, they discover a powerful weapon that the village is developing. They then have to decide whether to destroy it or take it for the Akatsuki. Along the way, they also have to deal with their own internal conflicts and the pressure of the mission.
The scrolls could hold secret jutsu. Uzumaki clan was known for unique abilities, so it might be something like a powerful sealing jutsu. Maybe Naruto discovers a new way to enhance his Rasengan using the knowledge from the scrolls.
He could face booby - traps. Sasori was a master of puppetry and defense, so he might have set up various traps to protect his workshop.
The OC could be designed as a very empathetic person. Since Sasori has a lot of emotional baggage from his past, an empathetic OC can understand his feelings and help him heal. For example, she could listen to his stories without judgment and offer comfort.
Naruto's character would evolve in many ways. He would gain a new sense of patience from working with puppets, which are delicate and require precision. His view of the ninja world would expand as he learns about Sasori's past and the history of puppet jutsu. This could lead to him being more empathetic towards enemies who have had difficult pasts. Also, his physical combat skills would be enhanced as he combines his existing ninjutsu with the puppet - based attacks he learns from Sasori, making him a stronger and more well - rounded ninja.