You could also create a scenario where the events of Prototype are a precursor to the events in Lord of the Rings. Maybe the destruction and chaos in the Prototype world led to some sort of magical rift that connected it to Middle - earth. And now, the consequences of the Prototype world's problems are spilling over into Middle - earth, forcing the inhabitants of both worlds to work together to solve the overarching issues.
A simple way would be to have a character from Prototype enter Middle - earth. They could bring their unique abilities, like super strength or shape - shifting, and use them against Sauron's forces. For instance, if Alex Mercer from Prototype was in Middle - earth, he could easily take on orcs and trolls in combat.
Another concept could be that a character from Lord of the Rings, like Legolas, somehow gets transported to the world of Prototype. There, he would have to adapt to the modern - day setting and deal with the infected. He could use his archery skills and elven agility in a completely different environment. His presence might also cause a stir among the military and scientific communities in the Prototype world, as they try to figure out who he is and where he came from.
Another approach could be a shared enemy. Suppose there is an entity that exists in both universes in a different form. Writers could create a story where the characters from Highschool DxD and Prototype have to team up to defeat this entity. This would require them to understand each other's powers and work together, leading to a lot of character development and exciting action scenes.
One way it could work is by having Naruto characters in Middle - earth. For example, Naruto with his shadow clone jutsu could be a great asset in the battles against Sauron's forces. He could create clones to confuse the orcs and trolls. Meanwhile, characters from 'Lord of the Rings' could learn from Naruto's ninja skills. Frodo might pick up some stealth techniques from Naruto's training.
In some fanfictions, technology might be introduced in a way that doesn't disrupt the magic of Middle - earth. For example, dwarves could use advanced mining technology that still has an old - world charm. It could be like steam - powered devices that work in harmony with their forges.
One way could be by having characters from 'Lord of the Rings' appear in the 'Game of Thrones' world. For example, Aragorn could show up as a mysterious ranger in the Seven Kingdoms. He might use his skills to navigate the political intrigue and power struggles, much like he did in Middle - earth.
Well, in a Naruto in a Lord of the Rings Harem Fanfiction, the story could start with Naruto being mysteriously transported to Middle - earth. Since he's used to fighting and protecting in his own world, he quickly gets involved in the conflicts there. As for the harem part, he might encounter Elven maidens who are intrigued by his strange powers and his unwavering determination. The harem could also include some strong human women who see Naruto as a powerful ally. They would all bond over their shared goals of protecting Middle - earth from the dark forces, with Naruto's ninja skills and positive attitude influencing them all.
One way to merge the storylines is through the concept of power. In Naruto, there is chakra, and in The Ancient Magus Bride, there is magic. They could find a way to exchange or combine these powers. Maybe a character from Naruto gets cursed and the only way to break it is by using the magic from The Ancient Magus Bride. This would force the characters to interact and learn about each other's worlds, thus merging the storylines. Also, the different cultures in both worlds, like the ninja clans in Naruto and the magical families in The Ancient Magus Bride, could be compared and contrasted, creating a rich and merged storyline.
First, you need to know both universes well. Read the books of 'Lord of the Rings' and watch the 'Avengers' movies multiple times. Then, think of an interesting concept for the crossover. For example, a magical object from Middle - earth getting into the hands of an Avenger. Next, focus on the characters. Make sure their personalities are consistent with their original versions. Don't just throw them together randomly.
Blake could be a bit of an enigma in Middle - earth. She might have some similarities to the Rangers, as she is used to being on her own and is very stealthy. Her faunus heritage could also add an interesting dynamic, as she could have some unique abilities that are different from the normal races in Middle - earth. Yang, with her strength and courage, would be a great addition to any battle. She could be like a female version of Gimli, always ready for a fight and not afraid to take on powerful enemies.
One way is to make the dragon lords the protectors of a powerful artifact. This artifact could be something like a magical key that can open portals between the two worlds. So the dragon lords, with their dragon companions, guard this key against those who would use it for evil in both the Harry Potter and Lord of the Rings universes.