There could be. The world of fanfiction is vast and full of diverse ideas. Some writers might be inspired to turn Aragorn into the Dark Lord as a way to subvert the traditional story. They might explore how different characters would react, how the story of Middle - earth would change, and what new plotlines could emerge from this radical transformation. But it may not be easy to find as it goes against the well - established character of Aragorn in the original works.
One possible theme could be the corruption of power. If Aragorn becomes the Dark Lord, it would show how easily power can corrupt even the noblest of characters. Another theme might be the fall of hope. Aragorn was a symbol of hope in the original story, so turning him into the Dark Lord would shatter that hope and explore the despair that would follow.
There might be a fanfiction where Aragorn is magically transported into the past when the Dark Lord was first rising to power. Here, he has to gather allies secretly as he is an unknown entity in that time. He uses his knowledge of the future to outwit the Dark Lord's minions and eventually finds a way to weaken the Dark Lord before he becomes too powerful, changing the course of history in a subtle way.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - created works, and you can use the search function to specifically look for Aragorn and Dark Lord fanfiction. Just type in relevant tags like 'Aragorn' and 'Dark Lord' and you'll get a list of stories.
I'm not sure if there are many Vampire Aragorn fanfictions out there. However, you could start by checking some popular fanfiction websites like Archive of Our Own. They have a large collection of Lord of the Rings fanfictions. You might need to use the search function and type in 'Vampire Aragorn' specifically to find relevant works.
The OC can be integrated through a common goal. For example, if the OC is a ranger from a different region but shares Aragorn's goal of protecting Middle - earth from Sauron. They can meet during a scouting mission and decide to combine their forces.
Another theme might be isolation. As a vampire in a world that mostly consists of non - vampires, Aragorn would probably face a great deal of ostracism. This could lead to a sense of loneliness and a search for his place in the world, much like his character's journey in the original Lord of the Rings but with a very different set of circumstances.
No. Aragorn and Legolas are good friends in the story. Aragorn is a man who is on a journey to claim his rightful throne and Legolas is an elf. They share a friendship that is built on their adventures together, their fight against evil, and their respect for each other's skills and cultures. There is no indication of a romantic love between them.
It could be a powerful, ancient Titan who was banished long ago and has now returned for revenge. Maybe Kronos has an even more evil and powerful form that he takes on, becoming the Dark Lord. He wants to destroy the new order of the gods and demigods that has been established since his last defeat.
One idea could be that the OC is a healer who joins Aragorn's journey. They meet during a battle where Aragorn is injured and the OC uses their unique healing skills to save him. This starts a bond between them as they travel together, with the OC providing medical aid to the whole fellowship.