One common theme is the adventure. Just like in the original works, characters from both universes often embark on grand adventures together. For example, Harry Potter characters might join the Fellowship of the Ring on their quest.
One common theme is the power of friendship. In both original works, friendship plays a huge role, and in fanfiction, it's often explored further. For example, in crossovers, characters from both universes form new friendships based on shared values.
One common theme is the corruption of innocence. Since Harry starts as a child, it shows how his initial pure and naive self can be influenced by the allure of dark magic. Another theme is the power struggle. As he becomes a 'dark lord', there are battles for control within the wizarding world.
One common theme is the clash of different magic systems. Harry Potter's magic is more about spells and potions, while the magic in Lord of the Rings is more ethereal. Another is the idea of a hero's journey. Both universes have characters on quests, and these fanfictions often combine those journeys.
Many fanfiction writers are attracted to dragons in these universes because they are such iconic and powerful creatures. In the context of combining Harry Potter and Lord of the Rings, a dragon could be a bridge between the two worlds, maybe a dragon that was once in Middle - earth but somehow ended up in the wizarding world of Harry Potter, creating all sorts of interesting storylines.
One common theme is power. As Lord Potter, Harry has more power, and fanfictions often explore how he uses or misuses it. Another is identity, as he has to adapt to this new title.
One common theme is the clash of different cultures. For example, when Middle - earth characters meet those from other fictional worlds, there are often misunderstandings at first due to different values and ways of life.
One common theme is self - discovery. Many original characters in the fanfiction are on a journey to find out who they are in the context of Middle - earth. For example, an OC might be a human with some elven blood and they are trying to understand both parts of their heritage.
One common theme is the clash of different powers. The high - tech powers of the Avengers against the magic in Middle - earth.
One common theme is the clash of different natures. Vampires, with their need for blood and immortality, are different from the races in Middle - earth. So, there's often a theme of how they are accepted or rejected. For example, elves might view them as abominations while humans might be more divided.
One idea could be a crossover where the characters from Harry Potter are transported to Middle - earth. For example, Harry could meet Aragorn and they could exchange knowledge about magic and leadership. Harry's magic could be a new and strange power in Middle - earth, and Aragorn's warrior skills and wisdom could inspire Harry.