Well, in the fanfic, Naruto might use the knowledge from the Forbidden Scroll to develop some unique and powerful jutsu. He could gain an edge in battles against his enemies like Orochimaru or Pain.
Jiraiya could be a crucial ally. As Naruto's mentor, he would be interested in the knowledge of the Forbidden Scroll. He could guide Naruto on how to use the knowledge safely and also protect Naruto from those who would try to take the scroll from him.
Well, it could be about Naruto finding the Forbidden Scroll and uncovering some long - lost jutsu that was sealed away for a reason. Maybe it's a jutsu that's too powerful or has some dark side - effect.
Maybe he's tired of being underestimated. Naruto has always been looked down upon in the village. Stealing the Forbidden Scroll could be his way of taking matters into his own hands and showing everyone that he's capable of great things. He might think that the secrets in the scroll will give him the edge he needs to change people's opinions of him.
Maybe a new character, created specifically for the fanfic. This character could be a rogue ninja who has heard rumors about the power of the Forbidden Scroll and wants to use it to take over the ninja world.
If Naruto steals the Forbidden Scroll in the fanfic, it's likely to set off a chain of events that will test his loyalty to the village. On one hand, he may be tempted to use the powerful techniques in the scroll for his own gain, like to get stronger quickly to defeat his enemies. But on the other hand, his sense of right and wrong, which has been instilled in him by Iruka and others, might make him realize that he has to return the scroll. Or, he could try to find a middle ground, where he uses just enough of the knowledge in the scroll to help the village in a time of need, without completely going against the village's rules.
It could also lead to him being targeted by enemies. If word gets out that he has access to the Forbidden Scroll's secrets, villains might come after him to either steal the knowledge from him or stop him from using it. This would put him in a lot of dangerous situations and force him to grow up quickly in order to protect himself and the village.
In some fanfiction, Naruto could use his shadow clone jutsu to create a distraction. While the clones are causing chaos, he slips into the room with the Forbidden Scroll and begins the copying process. He might also have some help from an unexpected ally who knows the security system around the scroll and helps him get access.
In fanfiction, if Naruto copies the Forbidden Scroll, he might gain extraordinary powers. He could learn some really powerful jutsus that are not accessible normally. This could make him extremely powerful overnight, changing the power dynamics in the story.
In some fanfictions, if Naruto keeps the Forbidden Scroll, he might discover powerful and forbidden jutsu within it. This could lead to him quickly becoming much stronger than his peers. He might learn some dark or extremely dangerous techniques that could change the course of his battles and relationships in the ninja world.