Well, it could be that Harry's hands - on experiences from his own time at Hogwarts make his teaching really engaging. He might share his encounters with dark creatures and how he overcame them. This could make Tom more aware of the practical side of DADA.
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.
As the teaching progresses, they could develop a sort of mentor - mentee relationship. Harry would be constantly trying to steer Tom away from the Dark Arts, while Tom would be trying to learn as much as he can from Harry. However, there would always be an underlying tension because of Tom's future as Voldemort. Their relationship might be a complex dance of trust and suspicion.
One possible plotline could be that Harry, with his knowledge of the Dark Arts from his own experiences, tries to show Tom the true nature of defensive magic. He might start by teaching basic spells like the Shield Charm. Harry could also share his insights on how to resist the allure of the Dark Arts, which is something Tom struggles with in his later years as Voldemort.
Maybe Harry would teach Tom about the consequences of dark magic. Since Harry has faced Voldemort multiple times and seen the destruction caused by dark spells. He could use these real - life (well, in the wizarding world) examples to make Tom understand that there are other paths in magic that are more positive and life - affirming.
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.
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.
A great fanfic idea could be that the DADA teacher is actually an animagus who uses their animal form to secretly spy on the Death Eaters. They could be a cat or a bird, for example. In the fanfic, Harry and his friends might start to suspect something strange about the teacher when they notice the animal always seems to be around when important information is being passed. Eventually, they discover the truth and the teacher becomes an even more important ally in their fight against the dark forces.
In this fanfiction, Sanguini could start by explaining the history of vampires in relation to the wizarding world's dark arts. He could talk about how vampires have been both feared and sometimes used as allies in battles against the dark side. Then, he could move on to practical lessons, like teaching students how to identify a vampire's lair and what precautions to take when approaching one. His lessons might also include how to use vampire fangs in certain potions for defensive purposes, making DADA a much more interesting and dangerous subject.
Well, in some fanfictions, Harry might draw on his own experiences facing dark magic. He could use his adventures with Voldemort as real - life examples to make the lessons more vivid. For instance, when teaching about defensive spells against the Imperius Curse, he could talk about how he resisted it in his encounters.
One challenge could be dealing with the traditional teaching structure at Hogwarts. The school had a set way of doing things, and Harry, with his more hands - on and unorthodox approach, might face resistance from some of the more conservative teachers. For example, they might not approve of his idea of using real - life dangerous situations as teaching examples.