Maybe Ichigo is a student at Hogwarts. He could be in a different house than the typical ones. He'd bring his sense of justice from the Bleach universe into Hogwarts and get involved in solving mysteries that involve both magical and spiritual elements. Like, there could be a Dementor - like creature that is actually a Hollow in disguise, and Ichigo would be the only one to notice the difference.
One idea could be that Ichigo is somehow transported to the wizarding world. He might use his Soul Reaper powers in unique ways against dark wizards. For example, his Zangetsu could be seen as a sort of magical weapon that even wizards are in awe of.
One idea could be that Ichigo has to go on a special mission with a group of characters and during the journey, they all discover new powers within themselves. For example, Ichigo could learn a new form of his zanpakuto from an unexpected ally.
Maybe in the fanfiction, Ichigo and Naruto meet during a tournament held in a world that combines the elements of their respective universes. They start as rivals but soon realize they have more in common and end up fighting together against those who want to disrupt the tournament for their own evil purposes. This could involve them combining their unique powers like Ichigo's Getsuga Tensho and Naruto's Rasengan in creative ways.
Maybe in a modern AU (alternate universe), Ichigo is a regular high school student and Lisa is a new transfer student. They meet in the library where Ichigo is studying for an exam and Lisa is looking for some rare books. Their initial encounter leads to a series of events that bring them closer together, like working on a school project.
One idea could be a story where Ichigo and Shirosaki are forced to team up against a new, powerful enemy that threatens both their existences. They have to learn to trust each other despite their differences.
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.