Well, I think Hinata would also be there to support Naruto. She's always been by his side and her Byakugan might be useful in detecting any strange changes in Naruto's body or chakra after breaking the seal. Also, Tsunade could play a role. As the Hokage, she has resources and knowledge. She could provide Naruto with protection if there are enemies targeting him because of the broken seal and also offer advice on how to handle the situation.
It'll likely change the power balance. If Naruto breaks the seal early in the fanfiction, the story could take a completely different turn. Enemies that were once a threat might become easy to defeat, or new, more powerful enemies could emerge because of the change in Naruto's power level.
In 'naruto breaks the seal fanfic', a consequence could be that Naruto has to deal with the sudden influx of power. He might struggle to control it at first, which could put himself and others in danger. Also, the secrets behind the seal could be revealed, which might involve some dark history related to his clan or the village. This could change how others in the village view him, either with more respect or more fear.
In the fanfiction, Naruto breaking the seal might also lead to him unlocking memories or abilities related to his family or the Uzumaki clan. He could discover secrets about his parents or ancestors that were sealed away. This could give him a better understanding of his heritage and purpose. It might also lead to him having new allies or enemies within the clan or among those who knew about the secrets of the seal.
Obviously, Sasuke would be affected. Since it's a Sasusaku - related fanfic, any change in Sakura would impact their relationship. He might have to adjust to a more powerful Sakura, or he could be worried about the consequences of the seal breaking.
Well, in such a fanfic, perhaps Sakura could gain new powers. With the seal breaking, she might be able to access a hidden reservoir of chakra. This could lead to her being more formidable in battle and changing the power dynamics within the Sasusaku relationship.
The Karma Seal can change Naruto's appearance. In some fanfictions, it might give him a more menacing look with strange markings spreading across his body.
Perhaps in this fanfiction, Naruto breaks a seal or a power that was related to Kushina. It could be a power that was passed down from her, but Naruto, in his journey to become stronger and more independent, decides to break it. This could have significant consequences for the plot, such as changing his abilities, his relationships with other characters, and his understanding of his heritage.
Another possibility is that it could be a new character created specifically for the fanfiction. A character who wears a mask for some secretive purpose, and when the mask breaks, it sets off a chain of events that are unique to the fan - created storyline.
Naruto might first be in denial. He would find it hard to believe that his mother would break a promise to him. But as the truth sinks in, he could become angry. He might lash out, either physically or verbally, at those around him who remind him of the broken promise. Eventually, he would probably turn this pain into motivation to prove himself despite the setback.