In a 'Harry is Sauron' fanfic, the plot could start with Harry having a strange encounter with an ancient artifact that links the two fictional universes. Once he becomes Sauron, he might initially be confused and horrified by the new power and the dark desires that come with it. The story could then revolve around his attempts to either embrace or resist this new identity. He could encounter characters from both universes. For instance, he might meet Frodo and be conflicted about whether to take the One Ring from him or protect him. Meanwhile, the wizards in the Harry Potter world might sense that something has happened to Harry and try to find a way to bring him back. This could lead to an epic adventure where different magical powers collide and Harry has to make some very difficult choices about his new role as Sauron.
Well, it could be that Harry somehow gets transported to Middle - earth and becomes Sauron. Maybe he has to deal with the power and the evil associated with being Sauron while still having some of his Harry Potter traits, like his sense of loyalty and courage, which could create an internal struggle.
One possible plot could be that Sauron somehow manages to enter the wizarding world. Maybe through a powerful dark magic spell that links the two universes. Harry, being the hero, senses the new and greater evil. He then has to figure out how to defeat Sauron, which is much more difficult than any foe he has faced before. He might have to learn about the power of the One Ring and how to destroy it, all while protecting Hogwarts and the wizarding world from Sauron's dark minions.
Well, one possibility could be that Harry discovers his true parentage as Sauron's son in a very shocking way. Maybe through some dark magic revelation. Then he might struggle with his identity, being a part of the wizarding world that he loves but also having this dark connection. He could face a lot of inner turmoil as he tries to decide whether to embrace his dark heritage or fight against it.
One possible plot could be that the fem Sauron, with her dark powers, infiltrates Hogwarts. She could initially be disguised as a new student or a teacher. Harry Potter senses something is off about her. There could be a series of magical duels and battles of wits between them as Harry tries to expose her true identity while she tries to carry out her own evil plans within the wizarding world.
In a 'Harry becomes Sauron' fanfiction, it might start with Harry being disillusioned with the wizarding world. He discovers some ancient magic that has a connection to Sauron's power. As he delves deeper, he becomes influenced by Sauron's will. He could then try to reshape the wizarding world in his image, which is now a dark and tyrannical one. He might even try to bring Middle - earth and the wizarding world together under his rule.
The plot could start with Naruto somehow being transported to Middle - earth. He quickly realizes the evil that Sauron represents. Naruto, being the hero he is, decides to take on Sauron. Along the way, he might team up with some of the local heroes in Middle - earth, like Aragorn or Legolas. They would be initially skeptical of Naruto but soon realize his power. Naruto would then engage in a series of battles with Sauron's minions, leading up to the final showdown with Sauron himself.
One possible plot could be that Harry Potter grows up in Mordor. Sauron might train Harry in dark magic, but Harry could have an internal struggle as he has an inherent sense of good from his parents. He might try to find a way to use the power he's learning for good, against Sauron's wishes.
In a fanfiction where Harry Potter fights Sauron, Harry would be at a disadvantage in terms of raw power. Sauron is an ancient and extremely powerful being. However, Harry has his courage and quick thinking. He could use his ability to solve mysteries and puzzles. He might figure out a way to destroy the One Ring, which would be a huge blow to Sauron. But it wouldn't be easy as Sauron would be constantly trying to stop him.
I'm not sure if there is such a specific 'Harry is Sauron' fanfic. Fanfic platforms like Archive of Our Own (AO3) might be a good place to start looking. You can search for relevant tags or keywords there.
One possible plot twist could be that Naruto has an inner struggle with the dark power of Sauron within him. Since Naruto is known for his positive energy in the original series, having this dark influence could lead to moments where he almost succumbs to evil but his friends' love and his own willpower pull him back.
Harry could be re - imagined as Sauron by having his personality shift. His usually kind - hearted nature could be warped by a powerful external force, like a dark spell or an encounter with a malevolent artifact. His magic could then be used for evil purposes instead of good, and he could start to see himself as a supreme being, much like Sauron does.