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 a fanfic, the curse marks could be a result of a failed jutsu they attempted together. The marks start to affect their chakra in unexpected ways. They find that they can no longer use their normal techniques as effectively. So, they have to train together in isolation to master the new power that comes with the curse marks. Along the way, they face their own demons and insecurities, and their relationship deepens as they rely on each other to survive and grow stronger.
You can try some popular fanfic websites like Fanfiction.net or Archive of Our Own. Just search for 'Naruto Sasuke curse mark' on their search bars, and you might find some relevant fanfics.
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.
The plot could be less centered around Sasuke's struggle with the curse mark's power and Orochimaru. Maybe there would be more focus on his normal ninja training and missions with Team 7. For example, he could be more involved in regular village protection tasks instead of being preoccupied with the curse mark.
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 Sasuke might become more withdrawn and brooding due to the power and dark influence of the curse mark.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.
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 type could be a fire - based curse mark. Given Sasuke's natural affinity for fire - style jutsu, a fire - based curse mark might enhance his existing abilities to an extreme level. It could make his fire jutsu more intense and uncontrollable at first. For Naruto, a wind - based curse mark could be interesting. Since he already has strong wind - style techniques, this curse mark might give him the ability to create more powerful and unique wind attacks, like a tornado - like jutsu with a dark twist.
Naruto's relationship with Sasuke could be really affected. Sasuke, having his own experiences with dark powers, might see Naruto in a new light. They could either become more competitive as they both struggle with different forms of dark power, or they could bond over their shared experiences of having something that sets them apart from others.
The 'sakura gets the curse mark fanfic' might focus on how Sakura's relationships change. Her friends could be worried about her. She may have to seek out ways to remove the curse mark, which could lead her on an adventure to find a cure. Along the way, she might discover secrets about the origin of the curse mark and its connection to some greater power in her world.
Well, a possible plotline is that the curse mark is linked to an ancient and dark power in the Naruto world. Naruto, with the curse mark, starts to have visions or dreams related to this power. As he tries to figure out what it all means, he also has to deal with the physical and mental toll the curse mark is taking on him. His training then becomes not only about getting stronger in general but also about mastering this new and dangerous aspect of himself.
Well, it could be about Hinata struggling with the new power and the negative effects of the curse mark. Maybe she has to learn to control it to avoid being consumed by its dark side.