He might struggle to adapt at first. In a muggle school, there are no magic classes or flying broomsticks. Harry would have to deal with normal academic subjects like maths and history. He'd also have to hide his magical abilities, which could be really hard when he's used to using magic for so many things in Hogwarts.
Well, he'd probably be a bit of an outcast. I mean, he has all this knowledge of the wizarding world and magic. At Muggle school, that doesn't really count for much. He'd have to hide his identity as a wizard too. And think about the subjects - no Potions or Defense Against the Dark Arts. Instead, it's all Math, Science, and English. It would be a huge adjustment for him.
In fanfiction, if Harry Potter goes to Muggle high school, it could be a chance for him to grow in a different way. He'd have to rely on his non - magical skills. Maybe he'd make some really good Muggle friends who would accept him for who he is. He could introduce them to some of the less dangerous aspects of the wizarding world, like Bertie Bott's Every Flavor Beans. It would be a whole new adventure for him, away from the usual wizarding threats.
Harry himself is obviously very popular. He's the main character in the original series, so in the 'Harry Potter Goes Muggle' fanfiction, readers are interested in seeing how he copes in the Muggle world. Hermione is also popular. Her intelligence and quick - wittedness make for interesting scenarios in the Muggle world, like helping Harry with Muggle studies.
One interesting plotline could be Harry trying to adapt to the Muggle world without magic. For example, he might struggle with simple things like using a computer or riding a bike, which would be hilarious. Another could be Harry introducing his wizard friends to Muggle culture, like taking Hermione to a Muggle concert or Ron to a football game.
His daily routine would be completely different. Instead of going to classes like Potions and Transfiguration, he'd be in Math and History classes. He might feel bored at times because he's used to the more exciting and magical learning at Hogwarts.
Well, there could be a lot of drama. Maybe some of the Muggle schoolmates were jealous of the wizarding kids back then. At the reunion, they try to cause trouble. Or it could be a really heartwarming story where the Muggle friends finally understand why their friends were a bit different. They might see how the magic has been used for good in the wizarding world, like helping the injured or protecting the innocent.
Yes, there are likely to be such fanfictions. The 'Harry Potter' universe has a vast and creative fanfiction community. Some fans might come up with the idea of Harry Potter being a Muggle assassin as a way to explore different storylines and character developments outside of the original canon. It could involve Harry using his magical skills in a Muggle - centered, assassin - like role, perhaps to protect Muggles from dark magic threats in a more covert way.
The 'harry goes muggle tournament' in fanfiction might be a story where Harry is forced or chooses to enter a muggle tournament for various reasons. It could be a way for him to prove himself in the muggle world or to gain a new perspective. If it's a physical tournament, he might have to train his body in a muggle way, which would be a big change for him. And he could also make new muggle friends during the process, which would further his understanding of the muggle world.
One big challenge would be the curriculum. He's used to learning about potions and transfiguration, but in a muggle school, it's all about things like science which is different from magic - based knowledge. Another challenge is fitting in socially. He might seem a bit odd to other students because of his wizarding background and different experiences.