There could also be a shadow - based curse mark. This might be more of a stealthy and sneaky type of power. Sasuke might be able to blend into shadows more easily and use them to his advantage in combat. Naruto could get a chakra - absorbing curse mark. It would allow him to absorb the chakra of his opponents during battle, which would be a huge advantage, especially against strong enemies in the fanfiction world.
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.
One common theme is power struggle. The curse marks give them both great power, but they have to learn to control it. Another theme is the bond between them. The curse marks can be seen as something that ties them together in a unique way. For example, they might share similar experiences related to the curse marks that make their relationship more complex.
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.
One interesting fanfiction is 'The Curse Marked Bond'. It delves deep into how Naruto and Sasuke's curse marks affect their relationship. It shows how they struggle with the power of the curse marks and how it both unites and divides them at different times. They learn to control the curse marks together and use their combined power to face new threats in the shinobi world.
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.
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 Sasuke might become more withdrawn and brooding due to the power and dark influence of the curse mark.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 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.
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.
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 is the 'what - if' scenarios. For example, what if Naruto failed to become Hokage? Another is the time - travel concept, where a character goes back in time and tries to change events. There are also AU (Alternate Universe) fanfictions, like a modern - day Naruto AU where the characters live in a contemporary setting.
One possibility could be that Sasuke is under a curse level 2 which affects his chakra flow. Sakura, being a skilled medical ninja, tries to find a cure. She has to face many challenges as the curse has some dark magic involved. Maybe she has to go on a journey to find rare herbs while also protecting Sasuke from those who want to use his cursed state for their own gain.