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.
One idea could be Sesshomaru arriving in Middle - earth in search of a powerful relic. He might cross paths with Aragorn and initially be seen as a threat. Another could be that he forms an alliance with the elves, as they both have an air of elegance and long - lived existence. Maybe he gets involved in the battle against Sauron, using his demonic powers in a way that surprises both friend and foe.
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.
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.
A lesser - known but excellent piece is 'Ringbearer Buffy'. Here, Buffy is somehow made into a ringbearer. It's a unique take on both franchises. The story delves deep into how Buffy's personality and her experiences as a slayer would affect her role in the quest to destroy the One Ring. It has some great character development and some really intense action scenes.
In a Harry Potter and LOTR crossover fanfiction, black magic could take on different forms. In the Harry Potter universe, it's often associated with the Dark Arts like the Unforgivable Curses. In LOTR, dark magic is related to Sauron and his minions. A crossover might explore how wizards from Harry Potter's world react to the more ancient and malevolent black magic of Middle - earth.
A popular one is 'The Meeting of Paths'. This fanfiction focuses on a situation where Inuyasha and Sesshomaru meet under different circumstances than in the original series. It has great characterizations, and the way the two interact and gradually change their views of each other is really well - written.
The main appeal is the combination of two very different but beloved universes. Buffy's world is modern, full of vampires and demons, while LotR is a high - fantasy epic. When they cross over, it creates a whole new set of possibilities. For example, seeing Buffy fight Orcs or Aragorn dealing with vampires is really exciting.
One way to blend the themes is through the idea of sacrifice. In LOTR, many characters sacrifice for the greater good, like Boromir. In Narnia, Aslan sacrifices himself. A fanfiction could explore how characters from both worlds understand and are affected by sacrifice. Also, the theme of the power of nature is present in both. The ents in LOTR and the talking animals and plants in Narnia can be part of a story that shows how nature can be a force for good against the encroaching evil in both worlds.
The appeal lies in the combination of two very rich and beloved fictional universes. Fans of both 'The Lord of the Rings' and 'Eragon' get to see their favorite elements come together. It's like a dream come true for many, seeing Aragorn interact with Eragon, for instance.