Well, in these fanfictions, the magical creatures in Harry Potter can be compared or even interact with Pokémon. The Hippogriff, for example, could be seen as a more magical version of a flying Pokémon. And the concept of magical potions could be used to create something that affects Pokémon in different ways, like a potion that makes a Pokémon stronger or more docile. The Portkey in Harry Potter could also be used to transport trainers and their Pokémon to different magical locations in the wizarding world.
Well, it combines the magical world of Harry Potter with the dark and alluring concept of a vampire king. In these fanfictions, the vampire king can bring a new type of power dynamic. For example, it might change the way magic is perceived or used in the story. The Hogwarts setting is also transformed as the vampire king's presence could disrupt the normal order. It's like adding a spicy new ingredient to an already delicious dish.
Well, it often blends the two by having characters from one universe enter the other. Like a Supernatural character might end up in the wizarding world through some sort of magical portal or spell gone wrong. Then they have to adapt to the new rules and powers there.
Well, magic in Harry Potter is very different from the powers of the Greek gods, but in fanfiction, they can be blended. For instance, the wands in Harry Potter could be seen as similar to the staffs that some Greek gods carry. The spells could be related to the incantations that the gods might use. Maybe a spell like 'Accio' could be seen as a weaker form of a god's power to summon things.
In these fanfictions, they blend by sharing certain characteristics. For example, the loyalty and camaraderie among the characters in both universes are emphasized. In Harry Potter, it's the loyalty among the students of Hogwarts and the Order of Phoenix. In Kancolle, it's the bond between the shipgirls. This common trait can be a basis for the two universes to interact, like the shipgirls and the wizards/witches working together based on mutual trust.
In fanfic, they can blend in various ways. For example, the magic systems can be combined. The runes from 'Mortal Instruments' might be used alongside spells from 'Harry Potter'.
Well, in some fanfics, the honor code of the Yautja might blend with the Gryffindor's sense of bravery. A Yautja might respect a Gryffindor who shows great courage in the face of danger, just as they respect worthy opponents in their own culture.
The worlds might blend through the use of shared magical elements. For instance, both have magical creatures. The gargoyles' ability to turn to stone during the day and come alive at night could be related to some form of Transfiguration magic in the Harry Potter world.
HPMOR blends science fiction elements with the Harry Potter world by introducing rational thinking. It makes the characters question the magic around them as if it were a scientific mystery. For instance, instead of just accepting spells as they are, they try to understand the mechanics behind them.
These fanfictions contribute to the fandom's creativity. Fans get to create their own versions of the wizarding world where James and Harry's relationship can be whatever they want it to be. It could be a more mentor - like relationship, or a very close friendship that defies the normal boundaries of time and space. This creativity spreads among the fandom, inspiring more people to write their own stories or create fan art based on these ideas.
One way to blend them is through the plot. Suppose there is a powerful dark force that is a threat to all three worlds. The heroes from Harry Potter, the Nephalem, and the characters from DxD would have to come together to fight it. The Nephalem could use their skills from their own world, like demon - slaying abilities, in the magical world of Harry Potter. In DxD, they could use the magical knowledge from Harry Potter to outwit their enemies. And the different cultures and power hierarchies from each world would create a rich tapestry for the fanfiction.