The wizard characters might initially be very cautious. For example, Hermione would likely be the one to do a lot of research on Muggle UN representatives and how to best communicate with them. She would probably try to find common ground in terms of goals like world peace and protection of all beings, magical or not.
In fanfiction, the Miraculous Ladybug characters could interact with the UN in multiple ways. First, they could be invited to give a presentation on the nature of akumas and how they've been combating them. Then, they might be part of a task force created by the UN to deal with a global akuma - like threat. Ladybug would use her leadership skills, while Chat Noir would bring his charm and combat skills. They would also interact with UN staff, learning about international laws and regulations regarding superhero activities. And perhaps they would even help in training other heroes from around the world who are brought together by the UN.
The interaction could be complex. The United Nations representatives in the fanfiction might try to coordinate efforts between different Countryhumans and the FBI. The FBI agents, on the other hand, would be used to a more direct approach. Some Countryhumans might be eager to cooperate with the FBI to show their loyalty to international law, while others might resist the United Nations' attempts at regulation. For example, a powerful Countryhuman might see the FBI's presence as an infringement on their sovereignty, but the United Nations would try to smooth things over and convince them to work together for the greater good.
Often, the wizard characters are curious about the Muggle girlfriend's world. They might ask her a lot of questions about Muggle technology like cars or mobile phones. And the Muggle girlfriend, in turn, is fascinated by magic, constantly asking for demonstrations.
Harry could take the girl to his favorite spots in the wizarding world, like Hogsmeade. He would have to be careful not to expose too much magic at once. They would interact with each other through sharing their different cultures, Harry's magical one and the girl's Muggle one.
Hermione would probably be very curious about Amaterasu. She would start researching about her in the Hogwarts library and try to understand her powers and her place in the other realm. Ron, on the other hand, might be a bit more cautious and a bit in awe. He would probably make some clumsy attempts at greeting her at first. Harry would be more open - minded. He might share his own experiences of facing powerful forces with Amaterasu and learn from her about her own battles against darkness.
Hermione would probably study Pokemon intently, making detailed notes about their abilities and behaviors. Ron might be a bit more hesitant at first but would warm up to them, especially if there was a Pokemon that he could share some food with. Harry would likely form a strong bond with a Pokemon, like he did with Hedwig, and they would go on adventures together.
Hermione would be very interested in studying Rapunzel's hair magic. She would want to research if it could be related to any known magic in the wizarding world. Rapunzel would be eager to learn from Hermione's vast knowledge of spells and potions. Ron might be a bit skeptical at first, but as he sees the practical uses of Rapunzel's hair, like using it to rescue someone from a high place, he would start to accept her and her magic. And together, they could face challenges like fighting off dark creatures or solving magical mysteries.
Harry might be initially cautious about the Triforce. He's used to his wand and magic, so this new, unknown power would be a bit intimidating. But his sense of right and wrong would lead him to explore its potential for good. He would likely try to use it to protect his friends and defeat Voldemort.
Harry would likely be very suspicious of The Joker from the start. He's used to dealing with threats in his own world, and The Joker's erratic behavior would set off alarm bells. Hermione would probably try to study The Joker, looking for a logical explanation for his actions and a way to counter him. Ron, on the other hand, might be a bit more fearful at first but would still stand by his friends. They would initially approach The Joker with caution, trying to figure out if he has any magical abilities or if he's just a very strange Muggle who has found his way into their world.
Sansa, with her refined manners, would initially seem a bit out of place among the more casual Hogwarts students. However, Harry would see past that and recognize her strength. They could interact in a way that Sansa teaches Harry about diplomacy and strategy from her own experiences in Westeros. Harry, on the other hand, could introduce Sansa to the concept of magic as a tool for good. Their interactions would also be shaped by their shared experiences of facing difficult situations and having to make tough decisions. They might even compare notes on how to deal with enemies like the Death Eaters and the Lannisters.