A more complex plot could involve a prophecy that links the two universes. Sesshomaru is initially seen as a threat by the wizarding world because of his demon nature, but as the story progresses, it is revealed that he is an important part of fulfilling the prophecy. Along the way, there could be cultural clashes between the two groups, with Sesshomaru's samurai - like honor code contrasting with the values of the wizarding world, and Harry having to mediate between them to achieve their common goal.
One possible plot could be that Sesshomaru somehow ends up in the wizarding world of Harry Potter. Maybe a magical portal or a powerful spell goes wrong. He then has to navigate this new world with its own set of rules and magic, and he might encounter Harry and his friends.
One plot idea could be that there is a strange magical - scientific anomaly that threatens both the wizarding world and the Watchmen's world. Harry and Jon have to team up to figure out what's going on and stop it. Maybe it involves a dark wizard using some sort of Watchmen - inspired technology to create chaos.
One idea could be that Sesshomaru somehow gets transported to the Harry Potter universe. He might initially be confused by the magic there which is different from his own demonic powers. He could encounter Harry and be both intrigued and a bit disdainful, seeing Harry as a young, inexperienced wizard compared to his own powerful self. But as time passes, they might have to team up to fight a common enemy that threatens both the wizarding world and Sesshomaru's own interests.
One plot idea could be that Mavis gets lost in the wizarding world and Harry has to help her find her way back to her own world. Along the way, they face various challenges like dark wizards who want to capture Mavis for her unique magic. Another could be that there's a threat that endangers both their worlds, and they must combine their powers to stop it. Maybe there's a powerful dark force that is trying to merge the two worlds in a chaotic way, and Harry and Mavis are the only ones who can prevent it.
One possible plotline could be that the female Harry Potter, through some magical accident or spell, ends up in the world of Inuyasha where she meets Sesshomaru. Their initial interactions might be full of mistrust, but as they face common enemies or challenges, they start to develop feelings for each other.
One plot could be that Harry Potter is bitten by a vampire during one of his adventures outside Hogwarts. He then has to struggle with his new vampiric nature while still trying to protect the wizarding world from dark forces. Another idea is that there is a hidden vampire community within the wizarding world that Harry discovers, and he has to deal with the politics and secrets there.
A possible plot could involve a spell gone wrong in the Harry Potter universe that opens a portal to the Hell Raiser world. As a result, some of the Hogwarts students get trapped in that terrifying realm. They then have to use their magic in new and creative ways to survive and find a way back home, all while being hunted by the hellish creatures. This could also lead to some of the Hell Raiser characters becoming interested in the power of magic and trying to take it for themselves.
Maybe the Sorting Hat could be used on the Transformers. The Autobots are sorted into Gryffindor for their bravery and the Decepticons into Slytherin for their cunning. Then a battle ensues within Hogwarts between the two factions, with the wizards caught in the middle, trying to keep the peace and protect their school.
Perhaps there's a prophecy in both universes that foretells of a coming disaster that can only be averted by the combined forces of the wizarding world and Riddick. Riddick is drawn to the wizarding world because of some strange magic that he senses. Once there, he meets Harry Potter. At first, they don't trust each other. But as they face challenges together, like strange magical - mechanical hybrids created by a rogue wizard who has been experimenting with technology from Riddick's world, they start to respect and rely on each other, ultimately working together to save both universes.
One possible plot idea could be how Snape deals with the physical and emotional changes during the pregnancy while still trying to maintain his role at Hogwarts. Another could be the reactions of other characters like Harry, Hermione, and Ron when they find out.
One possible plot could be that a Naruto character is transported to the Harry Potter world and has to let go of their chakra - based powers as they don't work there and learn magic instead, but they struggle with 'letting it die' i.e. their old way of fighting.