Maybe Castiel arrives at Hogwarts with a mission from the celestial realm to protect a particular student. While teaching, he subtly keeps an eye on this student. He could introduce new ideas about good and evil, different from what the wizards are used to, based on his angelic understanding. This could lead to some interesting debates among the students and faculty about morality and the nature of magic.
A plot could involve Castiel being a temporary replacement for a missing teacher. He brings his own strict yet fair teaching style. He might not be used to the mischievous nature of some Hogwarts students, like the Weasley twins. But instead of getting angry, he tries to understand their pranks from an angelic perspective and finds ways to channel their energy into positive magical experiments.
One possible plot could be Castiel trying to understand the unique magical system of Hogwarts. He might initially struggle as his angelic powers work differently. For example, he could be confused by the use of wands when he's used to his own celestial abilities. But as time goes on, he starts to blend his knowledge with the wizarding world's, creating new spells or teaching methods that combine angelic and magical concepts.
Harry Potter himself would be very interesting. Castiel could be intrigued by Harry's connection to Voldemort and his role as the 'Chosen One'. He might offer Harry some unique insights from his angelic knowledge about dealing with dark forces, which could be different from what Dumbledore has taught him.
Maybe Percy teaches Potions. He could start off by strictly following the textbook but then discovers a new potion ingredient while exploring the Hogwarts grounds. This discovery could lead to a whole new line of potions research in the fanfic. He would then involve the students in this exciting discovery, making potions class much more interesting than it was before.
Well, perhaps Percy could be teaching a new and difficult subject like Ancient Runes. He might use his strict and studious nature to get the students to really focus on the complex rune translations.
Perhaps the story could revolve around them facing challenges within the Hogwarts faculty. There could be some old - fashioned professors who oppose their modern teaching methods. Harry and Hermione then have to prove that their ways are beneficial for the students. They might also discover new magical abilities in some of the students that were previously overlooked, and help those students develop their skills.
Perhaps Harry is teaching Potions in the fanfiction. Since he had a bit of a rocky start with Potions in his student days, he could be a very understanding teacher. He might encourage students to experiment more, which is different from Snape's strict methods. He could also share stories about how important Potions were in his adventures, like when they made Polyjuice Potion. This would make the class more interesting and inspire students to take Potions more seriously.
Well, perhaps Harry Dresden could introduce his unique brand of magic from his own world into Hogwarts. He might teach the students new ways of dealing with magical creatures that are different from the traditional Hogwarts methods.
One possibility is that Merlin brings his ancient magic knowledge. He might introduce spells and magical concepts long forgotten in the Hogwarts curriculum. For example, he could teach students about pre - Hogwarts era potion - making techniques that are more in tune with nature.
The fanfic could be about a time - travel aspect of Castiel's proposal. He realizes that in order to have a future with his beloved, he needs to go back in time to fix some things. So, he travels through different timelines, experiencing various versions of their relationship. Along the way, he discovers what is truly important in their connection. When he finally comes back to the present, he proposes with a newfound understanding and depth of love, making the proposal a very profound moment that ties together all the different timelines and experiences they've had or could have had.
One possible plot could be that Ichigo and his friends from 'Bleach' are somehow transported to Hogwarts. They might initially be confused by the magic there as it's different from their own spiritual powers. Then, they could team up with the Hogwarts students to fight a common enemy, like a powerful dark wizard who is also dabbling in the realm of Hollows. Maybe the wizards help the 'Bleach' characters understand magic better while the 'Bleach' characters teach the wizards about their combat skills against Hollows.
Well, perhaps in the 'Naruto Mission to Hogwarts' fanfic, Naruto is invited to Hogwarts as part of a cultural exchange mission. He brings his ninja skills and chakra knowledge with him. There, he discovers that there are some dark forces at work in Hogwarts that are similar to the threats in his own world. So, he teams up with Harry Potter and his friends to fight against these new threats using a combination of ninjutsu and magic.