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.
At first, Sasuke would probably be very guarded. But Harry, being friendly, would try to break through that. Harry would show Sasuke around Hogwarts, and Sasuke might be a bit dismissive at first, thinking his ninja skills are superior. But as he sees the power of magic, he'd start to respect it. They would have conversations where Harry tries to understand Sasuke's past traumas, and Sasuke might be hesitant to open up. However, over time, they would bond, especially when facing a common enemy. Harry would use his quick thinking and magic, while Sasuke would use his combat skills.
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.
One possible plot could be that Harry, after his death in the Harry Potter universe, is reincarnated as Sasuke in the Naruto world. He would then have to deal with Sasuke's past traumas and his own new set of ninja skills and challenges. He might use his knowledge from the wizarding world in unexpected ways in the ninja world, like using magic - like spells that are disguised as ninja jutsu.
Naruto would adapt by being his usual enthusiastic self. He would be all over the place, asking questions, and getting into adventures. He might use his ninja agility to his advantage in things like Quidditch, even if he doesn't fully understand the game at first. Sasuke would be more cautious. He would study the magic system intently, comparing it to his ninja knowledge. He might have a hard time adjusting to the more laid - back atmosphere at Hogwarts compared to the intense ninja training environment he's used to. But as he starts to master some magic, he would gain confidence and start to feel more at home.
Sasuke could be a foreign exchange student of sorts. His Sharingan might be seen as a very rare and powerful magical ability. He would likely be very good at Defense Against the Dark Arts due to his combat skills.
Well, initially, there would be a great deal of disbelief. People would think it was some kind of elaborate prank. But once they realized it was real, there would be a wide range of reactions. The media in the wizarding world, like the Daily Prophet, would have a field day, with some journalists writing scathing articles and others being more sympathetic. Harry's enemies would likely try to take advantage of the situation, thinking he's vulnerable. But his allies, like the Order of the Phoenix, would stand by him and try to protect him and his unborn child from any harm.
Well, perhaps Sasuke's reincarnation is sought after by Voldemort. Voldemort hears rumors of a powerful being with strange and unknown powers (Sasuke's Sharingan and ninja skills). So he tries to either recruit or eliminate Sasuke. Sasuke, on the other hand, is more interested in finding out the secrets of magic in this new world and how it relates to his own past powers. He might form an unlikely alliance with Harry Potter to resist Voldemort, as they both have unique powers that the Dark Lord fears.
Well, it could be really interesting. Maybe Sasuke would teach Harry some ninja skills. Harry might grow up with a different kind of magic, a blend of wizardry and ninjutsu. He could use his wand in a more combat - like way inspired by Sasuke's fighting style.
Well, Naruto's ability to use chakra and his various jutsu like the Rasengan could be adapted in the High School DxD world in some interesting ways. Maybe his chakra could be seen as a unique form of magic. Sasuke's Sharingan and his ninja skills could also be tweaked. For example, the Sharingan could give him an edge in detecting the movements of devils and angels in that universe. He could use his ninja stealth to his advantage in battles or when sneaking around in the DxD high school setting.
It could be used as a plot device to bring characters from both universes together for a common mission. Say a powerful villain has hidden important items in both the Naruto and Harry Potter worlds, and the Portkey allows Harry and Sasuke to travel between the two to retrieve them all. They would have to rely on each other's unique skills to succeed.