One main theme is the clash of different worlds. Harry Potter's magical world and Giratina's Pokémon world are very different, so when they come together, there's a lot of exploration about how their rules and cultures collide. Another theme could be friendship. If Harry befriends Giratina, it shows how friendship can transcend different species and realms. Also, power and its proper use. Giratina is a very powerful being, and in the fanfiction, it often has to do with how that power is harnessed in the context of the Harry Potter universe.
One interesting 'Harry Potter Giratina Fanfiction' could be 'The Encounter of Harry and Giratina'. In this fanfic, Harry stumbles upon Giratina during one of his adventures in the Forbidden Forest. Giratina, being a powerful and mysterious Pokémon, creates a whole new set of challenges and opportunities for Harry. It's a great read for those who like to see crossovers between different fictional universes.
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.
The idea of different cultures and races coming together is also a big theme. Just think about the various species in Dragonlance and the different student groups in Harry Potter. Fanfictions often explore how they would interact, cooperate or even conflict with each other.
One main theme could be the battle between good and evil. Just like in the original Harry Potter series, but with the added element of the lich, which represents extreme evil. The story might show how Harry and his friends fight against the lich's dark intentions.