A really interesting plot could be a fusion of the two worlds. For example, the Hogwarts students are suddenly faced with Hollows attacking the school. The DADA professor, with their knowledge of both magic and the Bleach universe (maybe they have some past connection), has to train the students to fight in a new way, combining magic and Soul Reaper techniques. This would involve a lot of character development as the students adapt to this new threat and the new ways of fighting.
Perhaps the DADA professor is actually a reincarnated Soul Reaper. In the Harry Potter world, they have been suppressing their true powers. But as the story progresses, events start to trigger their memories and powers from the Bleach universe. They then have to balance their two identities, while also protecting Hogwarts from threats that are starting to emerge from the combination of the two universes, like dark wizards using Hollows for their own evil purposes.
Well, there are many great fanfictions out there. For 'Harry Potter' with a focus on the DADA professor, you can look on platforms like Fanfiction.net or Archive of Our Own. However, I'm not as familiar with specific crossovers with 'Bleach' in this regard. But generally, you can search for tags like 'Harry Potter DADA professor crossover Bleach' to find some interesting reads.
There might be a fanfiction where the DADA professor is actually an undercover wizard from a far - off land. He brings in unique teaching methods and magical creatures from his homeland, which both fascinates and challenges the students at Hogwarts.
One idea could be that Harry becomes a Defense Against the Dark Arts professor. He could use his real - life experiences to teach students in a more practical way. For example, he might take students on field trips to places where dark magic has occurred and show them how to detect and counter it. Another plot could involve Harry teaching a new subject, like Muggle Studies from a wizard's perspective, sharing his insights on the Muggle world he grew up in. He could also face challenges from some traditionalist professors who don't approve of his unorthodox teaching methods.
One idea could be a story where the professor discovers a long - lost magic within Harry that even Dumbledore was unaware of. This could lead to special training sessions between them, away from the prying eyes of other Hogwarts staff and students.
An interesting plot could be that the assistant professor is actually a time - traveler. They come from a future where Hogwarts is in ruins and are trying to change the past to prevent that future from happening. They might try to influence Harry and his friends in different ways to make sure they are better prepared for the upcoming battles.
One idea could be that Harry becomes a Defense Against the Dark Arts professor. He could teach students unique spells and techniques he learned from his own adventures. For example, he might introduce a class on how to combat dementors using the Patronus charm in more advanced ways. Another plot could involve Harry dealing with a student who has a connection to Voldemort, just as he did, and he has to guide the student to the right path. He could also face challenges from the school board who are skeptical of his teaching methods because of his unorthodox background.
One idea could be that the Death Eaters in the Harry Potter world somehow gain access to Hollow powers from Bleach. This could create a new kind of dark magic that the Order of the Phoenix has to deal with. Another plot could involve Hogwarts students being sent to the Soul Society for a special training exchange, and they have to adapt to the different spiritual powers and rules there. And perhaps a powerful Hollows attacks Hogwarts and the wizards have to team up with the Soul Reapers to defeat it.
Another challenge would be keeping up with the ever - evolving dark arts. Harry has had his share of battles, but new threats are always emerging. He would need to constantly study and research to stay ahead, so that he can teach his students the most effective ways to defend themselves. Also, he has to balance his duties as a professor with his own personal life and possible future adventures.
One interesting idea could be the combination of magic systems. In 'Harry Potter', there's wand - based magic, while in 'Bleach' there are spiritual powers. Maybe in the fanfiction, characters from both universes learn to use the other's power source. For example, Harry Potter could learn to use reiatsu (spiritual pressure from 'Bleach') to enhance his spells, or Ichigo from 'Bleach' could learn how to use a wand to focus his spiritual energy in a new way.
Another idea is to have the Death Eaters somehow get access to Hollow powers. This would create a whole new level of threat in the Harry Potter universe. The characters from Bleach could then be called in to help the Order of the Phoenix deal with this new threat. Harry Potter might learn some skills from Ichigo about combat and vice versa.