A fanfiction could focus on Harry Osborn's life at school. He's rich and popular, but in this version, he's also secretly dealing with family issues related to his father's business. He could cross paths with Peter more often at school, and their interactions could be a mix of rivalry and a budding friendship.
One idea is that Harry Osborn, jealous of Peter's popularity and heroics, decides to create his own alter - ego to compete with Spider - Man. But as he delves deeper into this new identity, he realizes that the world of superheroes is much more dangerous and complex than he thought, and he has to decide whether to continue or give it up.
The interaction of their powers would be fascinating. Harry's magic could be used to heal Spider - Man if he gets injured during a fight. Spider - Man's Spider - Sense could alert Harry of any oncoming danger, even magical threats that Harry might not be aware of immediately. Also, Harry could use spells to create distractions while Spider - Man uses his stealth to approach enemies unnoticed. This synergy between magic and superhuman abilities would create a very unique and exciting dynamic in the fanfiction.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions, and you can easily search for Peter Parker and Harry Osborn stories using the search bar. Just type in their names and you'll get a list of relevant fanfictions.
There's also 'Friendship Forged in Crisis' which is an amazing Peter Parker and Harry Osborn fanfiction. It focuses on a major crisis in the city where they have to rely on each other completely. The story has a lot of action and also some really touching moments between the two characters that really bring out the essence of their friendship.
Common themes in Harry Osborn Dehaan fanfic include the battle between good and evil within himself. He has the potential for both, and this internal conflict makes for great storytelling. Another theme is the exploration of his mental health. Dealing with the pressures of his life, he might struggle with things like anxiety or depression in some fanfics. And the theme of loyalty is also important, as he has to decide who he can trust and be loyal to among his peers and family.