A more complex plot could be a magical threat that affects both the Harry Potter world and the world of OHSHC. The characters from both universes have to team up. The Host Club members use their charm and unique skills, like Kyoya's intelligence in strategizing, along with the magical powers of Harry and his friends to defeat the threat. For example, the Dementors could start appearing in the OHSHC world, and they need to find a way to combat them using both magic and the Host Club's emotional support skills.
One idea could be that Harry Potter, somehow transported to the Ouran High School Host Club's world, has to hide his wizarding abilities while getting involved in the club's antics. Maybe he uses his magic subtly to help the club members in their personal problems, like using a spell to make Tamaki less clumsy during their hosting sessions.
Maybe Alucard is a time - traveler who accidentally ends up in the era of Harry Potter. He initially has his own agenda but gets involved in the fight against Voldemort. His unique powers, which are very different from the magic in the wizarding world, make him both an asset and a mystery. Harry and his friends are both fascinated and a bit afraid of him. Alucard could also introduce a new type of magic or power that the wizards have never seen before, which could change the balance of power in the war against the Dark Lord.
One idea could be that a character from Harry Potter, like Hermione, accidentally gets transported to Storybrooke. She could use her magic knowledge to help the residents solve a mystery that has been plaguing the town. Maybe it's a spell that has gone wrong and is causing strange things to happen, and her logical thinking and spell - casting skills would be very useful.
One idea could be that Slenderman somehow enters the wizarding world of Harry Potter. Maybe he's drawn by the powerful magic there. He could start causing strange disappearances in the Forbidden Forest, and Harry and his friends have to figure out how to stop this new, otherworldly threat using both their magic skills and their knowledge of the wizarding world's secrets.
One plot idea could be that a Kitsune disguises itself as a student at Hogwarts to learn more about human magic. It could get involved in Harry's adventures and use its Kitsune abilities, like shape - shifting or illusion - casting, to help or sometimes cause trouble. Another idea is that a Kitsune is a guardian spirit of an ancient magical place near Hogwarts, and Harry discovers it during one of his explorations. The Kitsune then becomes an ally or a guide for Harry in uncovering secrets about the wizarding world.
One idea could be that Shikamaru, with his strategic mind, gets transported to the wizarding world of Harry Potter. He could use his intelligence to help Harry and his friends in their battles against Voldemort. For example, he might come up with unique battle plans that the wizards hadn't considered before, like using the environment in Hogwarts in unexpected ways during duels.
Well, a plot could be Loki disguising himself as a Hogwarts student. He gets involved in the house rivalries and eventually meets Harry. They start off as adversaries but then realize they both have a common goal of protecting the wizarding world from a hidden danger. For example, an ancient evil that is about to be awakened. Loki could use his Asgardian knowledge and Harry his wizard skills to defeat it. Also, Loki could be interested in the magic of the wizarding world and want to learn more, leading to some humorous and interesting interactions with the Hogwarts professors.
Another plot could involve a crossover of villains. A dark wizard from the Harry Potter universe teams up with a criminal that the NCIS has been chasing. Harry Potter and the NCIS agents then have to join forces to stop this unholy alliance. They would need to combine their skills, with the wizards using magic and the agents using their detective and combat skills.
One plot idea could be Tonks helping Harry to master some of the more difficult Patronus spells. Since Tonks is a skilled witch, she could offer unique insights and training methods. Another idea is that they go on a secret mission together to find out more about Voldemort's hidden lairs. They might have to use Tonks' Metamorphmagus abilities to their advantage.
One idea could be that Harry is reborn into the world of 'Reborn' with his magical abilities intact. He could use magic to solve the mysteries and challenges in the 'Reborn' world, like helping Tsuna in a unique way. Another plot could involve the magic of the 'Harry Potter' universe somehow getting intertwined with the flames in 'Reborn'.
Another plot could involve Padme getting involved in the fight against Voldemort. Given her experience with political intrigue and combat in her own galaxy, she could bring a new perspective. Maybe she teams up with Hermione to research a way to defeat Voldemort using both magic and her own knowledge of strategy. They could discover a new spell or a way to undermine Voldemort's power base by using Padme's understanding of how to topple dictatorships.