The characters in both universes have distinct personalities. To blend the styles, you could have a character from Harry Potter develop a trait that is more common in Mochizuki's characters, like a more introspective and philosophical side. And vice versa, a character from Mochizuki's world could learn the sense of camaraderie that is so strong among the Hogwarts students.
One idea could be a crossover where the magical world of Harry Potter intersects with the unique universe of Jiro Mochizuki's works. Maybe Harry and his friends discover a portal that leads to Mochizuki's world and they have to adapt to new rules and powers there.
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.
One way is through the use of magical artifacts. In a 'Harry Potter science fanfiction', a time - turner could be studied from a scientific point of view. Scientists (wizard scientists) might try to figure out the physics behind traveling through time, looking at concepts like relativity and how magic circumvents them.
Authors need to first understand the core elements of both universes. For Harry Potter, it's the magic, Hogwarts, and the fight against Voldemort. In KHR, it's the Mafia families and the growth of Tsuna. Then, they can start by introducing characters from one universe into the other in a believable way. For instance, if Harry were to enter the KHR world, how would he adapt to the different rules and powers there?
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.
It can blend the two worlds by having the droids use their technological features in the wizarding world. For example, a droid's built - in map system could be used to navigate the complex corridors of Hogwarts. The droids could also introduce new concepts like energy sources that wizards might be able to adapt for their magic.
Character relationships are key. If a Hogwarts student befriends Quiet, they can learn from each other. The student can introduce Quiet to the concept of magic, and Quiet can show the student how to be more self - reliant in combat situations. This exchange of values and skills can help merge the two very different worlds of Harry Potter and MGSV.
One way is to establish a shared threat. Let's say there's a being that can travel between the two universes and is causing chaos in both. This forces the characters from Harry Potter and The Doctor to work together. In terms of world - building, describe how the different magics and technologies interact. For instance, the Time - Lords' time - travel abilities could be compared and contrasted with the time - turners in Harry Potter. The characters from both sides need to have believable reactions to the new elements of the other universe. Harry might be awestruck by the TARDIS, while the Doctor could be intrigued by the magic spells at Hogwarts.
A good way is to establish a common ground. For instance, if both universes have a form of magic, find a way to make those magics interact. Maybe Arturia's magic can be seen as an ancient form that has been forgotten in the Harry Potter world. Another way is through character relationships. Harry could look up to Arturia as a mentor figure, learning from her noble and chivalrous ways.