The curse mark can change their physical abilities. For Sasuke, it might enhance his speed and strength, but also make him more prone to losing control. Naruto, on the other hand, might develop new chakra - related powers because of his exposure to Sasuke's curse mark. For example, he could gain the ability to sense the curse mark's energy better.
One interesting plot could be how the curse mark affects their relationship. Maybe Sasuke's curse mark starts to make him more aggressive towards Naruto, but Naruto is determined to save him from its dark influence. This could lead to some intense battles and emotional moments between them.
In some fanfictions, the curse mark can initially drive a wedge between Naruto and Sasuke. Sasuke might become more withdrawn and brooding due to the power and dark influence of the curse mark. Naruto, on the other hand, would be worried about his friend but might not fully understand what Sasuke is going through. This could lead to some misunderstandings and arguments between them as Naruto tries to reach out while Sasuke pushes him away.
The curse mark could make Naruto more cautious. Since it's a dangerous and unpredictable power, he might think twice before acting impulsively as he usually does. For instance, in battle, instead of rushing in head - first, he'll consider the consequences of using the curse mark's power.
The curse mark could have a mind of its own. It starts to communicate with Naruto and Sasuke in their dreams, trying to manipulate them into doing its bidding. Naruto, being the optimistic one, tries to resist and turn the curse mark's power into something positive. Sasuke, however, is more tempted by the power it offers. This could lead to a rift between them as they have different approaches to dealing with the curse mark, and their relationship would be put to the test.
One great fanfiction could be where Sasuke's Curse Mark affects his relationship with Sakura in unexpected ways. Maybe it makes him more withdrawn and Sakura has to find new ways to reach out to him. For example, she might study more about the Curse Mark's origin to better understand what he's going through.
Their friends might be initially afraid of them. Since the curse mark is often associated with dark power, friends like Sakura and Kakashi could be worried that Naruto and Sasuke might lose control. This could create some distance between them as their friends are not sure how to approach them anymore.
One possible plot could be that they get the curse marks from a new, powerful enemy. They then have to figure out how to control the curse marks together without losing themselves to the dark power. Maybe they go on a journey to find a way to remove the marks while also facing challenges from other villages who see them as a threat because of the marks.
In some fanfictions, the Curse Mark Level 2 can grant enhanced physical abilities like super strength and speed. For example, the character might be able to move so fast that they seem like a blur to their opponents. It could also give the ability to manipulate certain elements more powerfully, like making fire hotter or water more forceful.
The curse mark in the fanfiction could be a catalyst for fem Naruto's growth. It could bring out hidden aspects of her personality. Maybe it gives her access to new powers that she has to learn to control. This process of learning and the physical and mental changes caused by the mark would surely have a profound impact on her character development. She might become more cautious, as she realizes the potential danger of the mark, yet also more bold in her attempts to master it.