For Harry, he could become more confident in his teaching abilities. He has always been a learner, but now he has to be the one imparting knowledge. The Marauders might develop a new respect for the importance of DADA. For instance, Sirius might see it as more than just a subject to goof around in. Remus could gain new insights into teaching methods that he can later use when he becomes a teacher himself at Hogwarts.
Maybe there will be a competition or a test in the DADA class that Harry is teaching. Tom could either shine or struggle, and this could affect his relationship with Harry. If he does well, he might gain more respect for Harry and DADA. If not, he could become determined to improve.
For Harry, he could become more in - depth in his understanding of Hogwarts' history and magic. Interacting with Helena Ravenclaw might make him more reflective and less impulsive. As for Helena, through her connection with Harry, she could gain a new perspective on the modern wizarding world and the changes that have occurred since her time.
Harry could also grow in his understanding of the wizarding education system. He realizes that there are many flaws in it. This understanding might lead him to want to make changes in the future, perhaps by influencing how magic is taught at Hogwarts or even in the wider wizarding world. He could start advocating for more inclusive and practical classes after seeing the limitations during his auditing experience.
One possible plot idea could be that Harry Potter, using his own experiences with dark magic and defense against it, teaches the Marauders new spells and strategies. For example, he could introduce them to the Patronus Charm in a more in - depth way than they might have learned on their own. Maybe he also shares his insights on how to deal with various dark creatures, based on his encounters in the Forbidden Forest.
Sanguini's character development could be centered around his transformation from an outsider figure to a respected teacher. At first, the other professors might be skeptical of him teaching DADA. But as he proves his worth through his unique teaching methods and knowledge, he gains their respect. He could also form special bonds with some students who are interested in the darker aspects of magic. He would teach them not only how to defend against dark forces but also how to understand and co - exist with them in a way, which is a very different approach compared to traditional DADA teachings.
In this fanfiction scenario, Harry would likely become more cunning in a positive way. He would have to use the Slytherin traits to his advantage while still maintaining his Gryffindor values. The Slytherin students would experience character growth as well. They might start to question their long - held beliefs about blood purity and house superiority. With Harry as their leader, they could become more collaborative with students from other houses, which would broaden their perspectives and make them more well - rounded individuals.
Draco could also change. Having Harry as his brother might make him more protective or more competitive. He might also start to see the flaws in his family's beliefs. As for other characters, Ron and Hermione might view Harry differently and their friendship could be strained or strengthened in new ways.
He might become more of a loner. Since his connection to Bobby Singer is not something the average wizard would understand, he could feel isolated. He may also become more secretive, hiding his knowledge from Bobby's world.
In this fanfiction, Harry teaching DADA could lead to some really creative storylines. He might invite some of his old friends, like Hermione or Ron, as guest lecturers. They could share their own knowledge and experiences, which would add a lot of variety to the classes. Also, Harry could start some sort of mentorship program for students who show a particular aptitude in DADA.
For Bellatrix, she could start to question her loyalty to Voldemort. Her interactions with Harry might make her realize that there's more to the world than just blindly following the Dark Lord. As for Harry, he could become more aware of the true nature of the Death Eaters at a very young age, which would shape his future battles. He might also develop a sense of pity for Bellatrix in a way, understanding that she's a victim of Voldemort's ideology too.