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.
Ron might be a bit skeptical at first. He'd be like 'What is this strange, talking pony doing here?' But as he got to know Fluttershy, he'd come to appreciate her kindness. For instance, Fluttershy could help Ron overcome his fear of spiders by using her gentle way of dealing with all creatures. And the Weasley twins would surely find some way to have fun with Fluttershy, perhaps by creating some harmless magical pranks that involved her unique pony - related magic.
Harry would likely be cautious at first. Alucard is a very different kind of being compared to the wizards he knows. Alucard, on the other hand, might be intrigued by Harry's magic. He could start by testing Harry's limits. But as they get to know each other, they might find common ground in their fight against evil. Harry could learn some of Alucard's more ruthless ways of dealing with enemies, while Alucard could understand the importance of friendship and loyalty from Harry and his friends.
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.