Yes, he might be. In some fanfiction universes, the author could reimagine Harry as the first Sith. This could be a really interesting twist on the original character, creating a whole new story arc full of dark side powers and different moral challenges compared to the traditional Harry Potter story.
Well, first, Harry would need to study the ways of the Sith. He has to understand his enemy. Then, he could combine his wizarding skills with some new knowledge. For example, he might learn how to use his magic to counter the Sith's mind - control abilities. He could also use his Patronus, which represents hope and light, to drive away the darkness of the Sith. And of course, he'd need to find the Sith's weakness, like in the way he found Voldemort's Horcruxes.
Sure. It could be that the plot centers around Harry's struggle to maintain his neutrality. He might be constantly tempted by the dark powers of the Sith but tries to use them for good or at least not for evil purposes. There could be a story arc where he tries to reform the Sith ideology from within, or perhaps he is on a quest to find a middle ground between the light side of the Force (like the Jedi) and the extreme dark side of the Sith.
Well, it could be his backstory. Maybe in this fanfiction, Harry has a really tough life that leads him down the dark path of the Sith. For example, if he's constantly betrayed or faced with extreme hardships that make him lose faith in the good side, he might turn to the Sith ideology.
A new character could be introduced as a Sith Lord. Maybe a wizard who has been studying dark and forbidden magic from other dimensions. He could have a red lightsaber - like wand and use powers that combine magic and Sith - like abilities. For example, he could use mind control not just on muggles but also on some weak - willed wizards.
I don't think it's a popular type of fanfiction. While there are many creative crossovers in the fanfiction world, the idea of making Harry Potter a sith pureblood is a rather strange and complex combination. It requires a deep knowledge of both the Harry Potter and Star Wars universes, and not many fans may be interested in such a convoluted mash - up. So it's likely not very popular.
I'm not entirely sure as it's a very specific and perhaps not a mainstream concept. But it might be a fan - created story where the Harry Potter universe is combined with elements of Sith (from Star Wars) and the idea of pureblood. It could be about a Harry Potter - like character who has Sith - like powers and is of pureblood heritage in this new, mashed - up fictional world.
One idea could be a story where a Sith Assassin somehow gets transported to the Harry Potter universe. Maybe they initially see it as a strange and weak world compared to their own, but then they discover the unique magic there. They could try to use their Sith powers to dominate, but find that the magic of Hogwarts and its defenders are not so easy to overcome.
One idea could be a crossover where a powerful Sith Sorcerer somehow finds his way into the Harry Potter universe. Maybe he's on a quest for a unique magical artifact that only exists in the wizarding world. He could start causing chaos, and the Hogwarts students have to figure out a way to stop him using both their magic and their knowledge of the wizarding world's secrets.
A common theme is the struggle between good and evil. Since Harry is usually the main character who gets involved with Sith - like elements, it shows his internal battle between his original good - natured self and the dark influence. For example, in many of these fanfics, he might struggle with using dark magic for what he believes are good reasons.