The themes often revolve around power and responsibility. Harry is used to his own set of magical rules and powers, and Paige has hers. When they come together, they have to figure out how to use their powers responsibly in this new combined situation. Also, discovery is a theme. They are both discovering new aspects of magic and each other's worlds.
One popular 'Harry Potter and Paige Matthews fanfiction' is 'The Magical Convergence' which combines their two worlds in an interesting way. It has a great plot that involves Paige using her magic to help Harry in his fight against Voldemort. Another one could be 'A World of Magic and Witches' where their different magical abilities interact and create unique storylines.
Espionage is a major theme. His novels are set in the world of spies, showing how different intelligence agencies operate and compete.
Growth is a common theme. Many fanfictions focus on how Joshua matures over time, like dealing with career choices or relationship issues.
One of the main themes is power and its consequences. When the Rinnegan, which is a very powerful ability, is introduced into the Harry Potter world, it often explores how having such power can affect the character's relationships and their place in the wizarding society.
Faith and hope are also prominent themes. The characters might find strength in their faith, whether it's in a higher power or in the goodness of others. For instance, when facing difficult situations like the threat of Voldemort, they hold on to hope and believe that good will ultimately triumph, which is similar to the Christian belief in God's plan and the victory of good over evil.
One main theme is the clash of different power systems. Since the Kyuubi has its own set of powers from the Naruto universe and Harry Potter has magic, seeing how they interact and sometimes clash is a big theme.
Another theme is power and its corrupting influence. Circe is a very powerful witch in Greek mythology, and when she meets Harry, there's often a struggle for power or a test of who can resist the allure of more power. This can be seen in fanfictions where Circe tries to manipulate Harry into using dark magic for her own ends.
Self - discovery is a major theme. In many such fanfictions, characters like Harry are on a journey to find out more about themselves, their powers, and their place in the wizarding world. For instance, they might discover hidden magical abilities they never knew they had.
Magic and transformation also play important roles. The magic in the 'Harry Potter' world is used in new ways to symbolize the character's internal transformation. For example, a transfiguration spell could be used as a metaphor for the character's physical and mental transformation, which is really creative and adds a new layer to the fanfiction.
One main theme is the clash of cultures. The magical and often more civilized world of Harry Potter against the wild and war - like Dothraki culture. For example, in many fanfics, the Dothraki's view on honor and combat is contrasted with the values of the wizarding world.