She could survive by being away from the village during the massacre. When she returns, she is shocked. She decides to investigate the real cause of the massacre. Along the way, she discovers some dark secrets about her clan and the village. This knowledge gives her a new purpose, and she uses her Uchiha powers to bring the truth to light.
Perhaps she is saved by an unexpected ally. This ally could be from another clan or even a hidden organization. She then has to learn to trust this new ally while also dealing with her grief and anger over the loss of her clan. She might also discover new powers within herself as she struggles to survive in a world that has become very hostile to her.
She would change the story because she would be a target. Those who caused the massacre would want to finish the job. This would lead to many chase and escape scenes. Also, other characters would be divided in their opinions about her. Some would see her as a threat, while others would see her as a symbol of resistance.
One possible plot could be that after surviving, Female Noble Six becomes a mentor. She uses her skills and experiences from the battles she's endured to train new recruits. Maybe she starts a secret mission to uncover the truth behind the events that nearly cost her her life, all while evading the enemy who still wants her dead.
The Otsutsuki OC could be a catalyst. They might have some knowledge about the future or some power that the Uchiha want. This could lead to internal strife within the Uchiha clan as some members might be tempted to side with the OC for power, while others oppose it, which could be a contributing factor to the massacre.
One possible plot could be that Dr Strange uses his magic in a way that shields him from the snap's effects. Maybe he creates a temporal or dimensional bubble around himself just in time. He then has to figure out how to reverse the snap while dealing with the chaos that ensued. He might travel through different dimensions to find a solution or seek help from other powerful entities.
One possible plot could be that Naruto discovers he has some Uchiha blood in him. This revelation would change his perspective on himself and his place in the ninja world. He might then start to train more intensively to master Uchiha abilities.
Maybe Naruto secretly admires the Uchiha's Sharingan ability and tries to learn more about it on his own. He could be collecting information about the Uchiha clan's history and techniques without anyone knowing.
One possible plot could be that Sakura, reborn as an Uchiha, discovers new powers within herself. Since the Uchiha are known for their Sharingan, she might struggle to control this powerful dojutsu at first. She could face challenges from within the Uchiha clan as some might not accept her, seeing her as an outsider who has suddenly become one of them. Along the way, she might also have to deal with the typical Naruto -verse threats like Akatsuki, but with her new Uchiha abilities, she could offer a different perspective and set of skills to combat them.
One interesting idea could be how the themes of sacrifice from Itachi's story in Naruto might be translated into the RWBY universe. For example, Itachi sacrificed his reputation and relationships for the greater good of his village. In RWBY, a character might have to make a similar choice between personal relationships and the safety of the kingdoms. Another aspect could be the combat styles. If Itachi were to exist in the RWBY world, how would his Sharingan abilities blend with the Dust - based combat? It could lead to some really creative fight scenes. Also, the concept of family loyalty, which is strong in Itachi's story, could be explored in relation to the families in RWBY like the Rose or the Schnee families.
One way is to make the Otsutsuki OC a hidden observer during the Uchiha massacre. They could be there to study the Sharingan or the power dynamics within the Uchiha clan. For example, they might be interested in how the Uchiha's emotions, like hatred, are related to the power of their eyes. Another way is to have the OC be a factor that somehow influences Itachi's decision. Maybe they offer him a different option or some knowledge that makes him rethink his actions, but in the end, the massacre still occurs due to the complex web of political and clan - related reasons in the Naruto universe.
The Otsutsuki OC might be an unexpected bystander during the Uchiha Massacre. For example, they could have been on a different mission in Konoha when the massacre started. They might then decide to get involved, either to save some Uchihas out of a sense of justice or because they see potential in the Uchiha bloodline for their own purposes. So, they end up interfering with Itachi's plan and creating a whole new set of consequences for the story.