To blend these two worlds in a fanfic, consider the magic systems. In the 'Harry Potter' world, magic is more about incantations and wand - waving, while in Fma, it's about understanding and manipulating matter through alchemy. You could create a scenario where the two magics start to merge. Maybe due to a magical accident, some wizards gain the ability to perform alchemy and vice versa. This would lead to a lot of chaos and discovery as the characters from both worlds have to adapt. Also, the cultures of the two worlds could be mixed. The strict social hierarchy in the Fma military could be compared and contrasted with the house system at Hogwarts, and this could be a source of conflict or cooperation among the characters.
One way to blend the worlds is through a common threat. Imagine a powerful dark force that can only be defeated by combining the powers of alchemy and wizardry. This would force the characters from both universes to come together. For example, a new type of dark magic that is based on the principles of alchemy but is much more dangerous. The characters would need to figure out how to use their unique skills to combat this threat. Another aspect could be the exploration of different dimensions. Suppose there is a way to travel between the Fma world and the 'Harry Potter and the Cursed Child' world through some sort of magical - alchemical portal. Characters could accidentally end up in the wrong world and have to find their way back while dealing with the differences in culture and magic.
The simplest way is through character crossovers. Have characters like Harry or Hermione meet and interact with Edward or Alphonse. They could exchange knowledge, with the Fma characters explaining alchemy and the Harry Potter characters sharing about magic spells. Another way is to blend the settings. For example, have Diagon Alley also include alchemical shops selling items like philosopher's stones or transmutation circles.
Some characters from Fma would approach the magical creatures with a sense of wonder and a desire to learn. They would try to find alchemical explanations for their abilities. For instance, a character might see a Phoenix and wonder if its ability to be reborn is related to some form of alchemical regeneration. They would also likely compare the magical creatures to the chimeras and other strange creatures they are familiar with in their own world. This would lead to some interesting cultural exchanges between the two universes as they try to understand and interact with the magical creatures.
One idea could be to have characters from Fma use their alchemy skills in the wizarding world of Harry Potter. For example, Edward could try to analyze the magical properties of potions using his knowledge of equivalent exchange. Another idea is a crossover of the villains. Maybe Father from Fma teams up with Voldemort, creating a more complex and dangerous threat for the heroes of both worlds to face. It could also be interesting to see how the Philosopher's Stone and the power of alchemy interact, like if the stone could be used to enhance alchemical processes or vice versa.
One idea could be that characters from Fma use their alchemical skills in the wizarding world of Harry Potter. For example, Edward could try to transmute a magical object using his knowledge of equivalent exchange. Another plot idea might be that the Philosophers Stone from Harry Potter has some connection to the alchemy in Fma, and characters from both universes have to work together to protect it from dark forces. Also, perhaps a character from Fma gets sorted into one of the Hogwarts houses and has to adapt to the magical school life while still having their own alchemical powers.
The worlds can be blended by having Barbie visit Diagon Alley. She could be amazed by all the magical items and use her fashion sense to customize her wizarding robes. For instance, adding some sparkly elements that are typical of Barbie's style.
The blend can occur through the use of magic in relation to trigonometry in solving problems. For example, in a fanfiction, a magical creature is lost in a forest that is magically generated with trigonometric patterns. The characters need to use their knowledge of both magic and trigonometry to find the creature. Also, a character's magical power could be related to their understanding of trigonometry, so as they learn more math, their magic becomes stronger and more versatile.
A great way to blend the worlds is through a shared threat. A villain that uses both magic and technology to cause chaos. This would force Harry and Tony to work together. They would have to learn from each other's strengths and overcome their differences. Harry could teach Tony about the subtleties of magic, while Tony could show Harry how to use technology to gain an edge in battle.
In fanfiction, the characters could also meet during a special event. For instance, there could be a magical music festival that attracts both wizards and Muggles. Harry Potter and his friends are there for the magical elements, while Hannah Montana is performing. They cross paths and end up collaborating on a song that has magical properties, like making everyone who hears it feel extremely happy.
One way is through a portal. For example, a magical portal could open up between Hogwarts and Neverland. This allows characters from both worlds to interact. Harry Potter could enter Neverland and be shocked by the lack of traditional magic but also find unique magical elements there related to the island's magic. Captain Hook could enter Hogwarts and be amazed and also threatened by the powerful magic there.
Themes can be merged. The theme of good vs evil is present in both. In fanfiction, the dark wizards from Harry Potter could team up with the more malicious vampire clans in Rosario Vampire to create a super - evil force. And the heroes from both worlds would have to join forces to stop them. This would require characters to look past their initial differences and prejudices to fight for the greater good.
Well, you could start with a magical portal. A Uzumaki character, known for their strong chakra, accidentally opens a portal that leads to the Harry Potter world. An Uchiha, with their Sharingan, could be drawn to this portal as well, sensing the strange new magic. Once in the Harry Potter world, they could learn magic, and maybe even teach some of their ninja skills to the wizards.