In fanfiction, Harry Potter's adaptation to the American wizarding world would be a complex process. He would have to deal with cultural differences, like the way American wizards celebrate holidays. He may find that the American wizarding community has a different attitude towards Muggle - borns. Also, the architecture of American wizarding buildings and the layout of their magical cities could be very different from what he's known in the UK. All these factors would require him to be open - minded and flexible in order to fully adapt.
Harry would need to learn about the different magical laws in America. For instance, the regulations regarding magical creatures might be stricter or more lenient compared to the UK. He might also have to get used to the different currency used in the American wizarding economy.
Sasuke's adaptation would be a long process. He'd start by observing the daily lives of wizards. He'd notice how they use magic for simple tasks like lighting candles or cleaning. In contrast, in his past life, he'd use ninjutsu for such things. He'd have to get used to the fact that he can't just rely on his Sharingan all the time. He might attend classes at Hogwarts and learn about different spells. At the same time, he'd be constantly comparing the magic here to his ninja skills. As time goes on, he'd start to blend in more, using magic in his own unique way that combines his ninja - like thinking.
He'd probably use his magical training to his advantage. His physical fitness from all the running around Hogwarts and fighting dark forces would help him on the pitch. Also, his ability to stay calm under pressure, like when facing Voldemort, would be useful during important soccer matches.
Well, at first, Felicity might be a bit out of place. However, her skills with technology could give her an edge. She could start by trying to understand the magical energy as a form of power source. Maybe she would try to create some sort of device that could detect different types of magic. In terms of social adaptation, she would probably befriend Hermione quite quickly as they both have a thirst for knowledge. And she would gradually get used to the customs of the wizarding world, like the use of Floo powder and Apparition, though she might try to find a technological explanation for these things at first.
In this fanfiction, the Harry Potter characters would first be amazed by the physicality of Eyeshield 21. But they would adapt. Neville could use his new - found confidence to be a great blocker on the football field. Luna could see things from a different perspective and suggest unorthodox but effective plays. And Dumbledore, if he were to be involved, could be like a wise coach, guiding the characters through the challenges of this new sport and world.
The Order of the Phoenix would immediately spring into action. They would start searching for Harry using all their magical resources, including spells like the Tracking Charm. Dumbledore would likely be at the forefront, using his vast knowledge and connections to try and figure out where Loki has taken Harry.
The wizarding world would likely be plunged into a state of despair. Harry was seen as the 'Chosen One' to defeat Voldemort, so without him, there would be a sense of hopelessness. Voldemort would probably have free rein to impose his dark rule without much opposition at first.
They could fit in as strange visitors from another dimension. The wizards would be both curious and cautious about them. Maybe the Guardians are there to trade some unique galactic items for magical artifacts.
The wizarding world would be in an uproar. Phylacteries are associated with dark magic. Harry is seen as a hero, and for him to create a phylactery would shatter the image. The Ministry of Magic would likely brand him as a dark wizard or at least someone who has strayed too far from the light. His friends would be divided. Some might try to defend him, believing there was a good reason, while others would be horrified and distance themselves.
Some in the wizarding world might be very accepting. For example, Dumbledore, being a very open - minded and wise wizard, could offer his support and guidance to Harry. He would see Harry as the same person regardless of the change. However, there would also be those who are more traditional and conservative, like some of the pure - blood families. They might shun Harry or try to find a way to 'fix' him, believing that this change goes against the natural order of the wizarding world.
The wizarding world would be in shock. People who once idolized him would feel betrayed. The Ministry of Magic would probably declare him a most wanted wizard and send out Aurors to capture him.