Another theme is self - discovery for Harry. With the influence of the MC, Harry gets to explore different aspects of himself. For example, he might discover new magical abilities or gain more confidence in his identity as a wizard. In some fanfictions, the MC helps Harry to look beyond what he thought was possible for himself.
One popular 'Harry Potter MC Adopts Harry' fanfiction is 'A Different Sort of Home'. In this story, the main character takes Harry in and provides a nurturing environment that is quite different from what he experiences in the Dursley's household. It delves into how Harry's character develops in this new setting, with the MC teaching him magic in unique ways and introducing him to a different side of the wizarding world.
Perhaps Bruce Banner adopts Harry Potter after the events at Hogwarts. He takes Harry to the world of science, showing him things like advanced laboratories and scientific research. Harry, in turn, shows Bruce the wonders of magic. Their bond grows as they learn from each other, and together they face new threats that combine elements of both the magical and scientific worlds.
It could be a young wizard who lost their parents during the final battle against Voldemort. Harry feels responsible for all the orphans created by the war and decides to take this particular child under his wing.
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.
The MC could prevent some tragedies. For example, if they have the ability to foresee the future, they might be able to stop Cedric Diggory from being killed by Voldemort in the Triwizard Tournament.
The MC (main character) can be a new student at Hogwarts. They could be sorted into one of the houses and experience all the magical adventures like learning spells, exploring the Forbidden Forest, and making friends with the well - known characters in the Harry Potter world.
Batman's brooding and serious personality would likely make Harry more cautious. Batman is all about planning and preparation, and Harry would pick up on that. For example, Harry might start to analyze magical situations more thoroughly before acting, instead of just relying on his instincts.
His magical abilities might develop in a different way. The Malfoys could introduce him to different types of magic or magical artifacts. Maybe he'd learn more about the Dark Arts in a different context, not for evil purposes but just to understand it better. He could also become more skilled in areas like Occlumency earlier on, since the Malfoys might see it as an important skill to protect their family secrets. His relationship with his Gryffindor traits would be tested. He might still have his bravery, but it could be expressed in different ways, like standing up to the Malfoy family's wrongdoings.