In 'lotr slash fanfiction', a recurring theme is the idea of forbidden love. Given the cultural and social structures within Middle - earth, relationships that deviate from the norm, like a relationship between two male characters from different races or social standings, are often explored. This adds an element of tension and drama. Another common theme is the power of love to overcome differences. Whether it's differences in race, like an Elf and a Dwarf in a relationship, or differences in personality, love is often shown as a force that can bridge these gaps.
One popular 'lotr slash fanfiction' is 'The Ties That Bind' which explores the relationship between Legolas and Gimli in an interesting new way. It delves deep into their friendship and how it could potentially be more. Another one is 'A Different Path' that focuses on Aragorn and Boromir. It's a great read for those who like to see different character dynamics within the LOTR universe.
Another way is to join fanfiction communities or forums dedicated to either Harry Potter or LOTR. Members there might be able to recommend some great slash fanfictions that combine the two. They may also share their own works or works in progress that are of this type.
One idea could be a demon from the 'demon' world gets transported to the HP and LOTR universes. It could befriend a Hogwarts student and then together they end up in Middle - earth. Maybe the demon has some unique powers that help in the battles against Sauron. For example, the demon might be able to sense the presence of the One Ring from afar. And the Hogwarts student could use their magic in ways that are new to Middle - earth, like using a levitation charm to move large boulders during a siege.
There are fanfictions that play with the idea of time - traveling or dimension - hopping between the two universes. In these stories, characters like Hermione and Gandalf might cross paths. They could exchange knowledge, with Hermione learning about the ancient magic of Middle - earth and Gandalf getting insights into modern wizardry. This often leads to very interesting and complex plotlines in the slash fanfictions.
In terms of the slash relationships, a wizard from HP might fall for an elf or a human from LOTR. Their different magical abilities and cultures would create an interesting dynamic. The demon, if it has a more benevolent nature, could act as a mediator between the different groups. It could use its knowledge of different planes of existence to help the characters understand each other better. For instance, it could explain to the wizards how the magic in Middle - earth is different but still related to their own magic in some ways.
One idea could be that the One Ring somehow ends up in the world of Pirates of the Caribbean. Jack Sparrow, being the wily character he is, gets wind of its power and decides to either use it for his own gain or sell it to the highest bidder. The Fellowship, in turn, has to track it down in this strange new world full of pirates, sea monsters, and cursed treasures.
Lotr has a huge fan base already, and when you add the element of vine fairies, it's like opening a new door to creativity. Writers can create all sorts of scenarios where the fairies interact with the hobbits, dwarves, etc. It gives a fresh perspective on the well - loved Lotr world.
Definitely Legolas and Will Turner. Legolas with his amazing archery skills could teach Will some new techniques, and Will could show Legolas the ropes of being a pirate. They both have a sense of honor and loyalty, so they would make an interesting duo.
Sesshomaru's speed and agility would be a great asset in Middle - earth. He could easily outrun orcs and other foes. His sword, Tenseiga, which has the power to resurrect, could also have an interesting impact. For example, if he were to use it on a fallen hero, it could change the course of a battle.