A Bleach and One Piece crossover would also be cool. Imagine the Straw Hat Pirates arriving in the Soul Society. Luffy might try to befriend some of the Soul Reapers, and Zoro could have an epic sword - fighting match with one of the more skilled Soul Reapers. Usopp could also be amazed by the different spiritual powers at play.
Another possibility is a Bleach and Harry Potter crossover. How about the wizards from Hogwarts visiting the Bleach universe? They could use their magic to interact with the spiritual entities there. Hermione might be fascinated by the complex spiritual hierarchies and try to study them, while Harry could use his Gryffindor courage to face some of the Hollows.
Well, you could focus on the character crossovers. Imagine Jotaro Kujo meeting Ichigo Kurosaki. Jotaro's cool and collected demeanor would contrast with Ichigo's more hot - headed nature. They could learn from each other's fighting styles. And then there's the possibility of Stand users having to adapt to the spiritual energy in the Bleach world and vice versa. This could lead to some really interesting power - up and training sequences for the characters involved.
One idea could be a scenario where Naruto and Ichigo meet in a dimension between their worlds. They initially misunderstand each other due to their different combat styles and powers. Naruto might mistake Ichigo's Zanpakuto for a strange kunai at first. But then they realize they are both protectors of their respective realms and team up to face a common threat that is endangering both the Naruto and Bleach universes, like an ancient evil entity that feeds on spiritual and chakra energy.
A great 'bleach crossover fanfiction' idea is to cross it with One Piece. The Straw Hat crew could end up in the Soul Society. Luffy's carefree attitude would contrast with the more solemn Shinigami. Also, a Bleach and Fullmetal Alchemist crossover where the alchemic principles are applied in the Bleach universe would be really interesting.
One idea could be that Ichigo and Maka meet in a dimension that is a blend of their two worlds. They initially mistake each other for enemies but then realize they have a common goal of fighting against a new type of evil that is emerging due to the merging of their universes. Another plot could involve the Soul Reapers and the Meisters exchanging their powers for a short time to better understand each other's fighting styles and learn new techniques. A third plot idea is that the Hollows in Bleach start to target the souls in the Soul Eater world, and the characters from both series must team up to stop this invasion.
One idea could be to explore an alternate timeline where Ichigo never became a Soul Reaper. Maybe he lives a normal life, but strange spiritual events still occur around him, drawing him into the world of the Hollows and Soul Reapers in a different way. Another idea is to focus on a side character, like Uryu, and tell a story from his perspective during a major arc that we didn't see much of in the original series. For example, his experiences during the Arrancar arc when he was off on his own missions.
Perhaps there is a crossover of the worlds where the Hollows start attacking the One Piece islands because they sense a large amount of spiritual energy there. The Soul Reapers follow them and have to work with the local pirates, including the Straw Hats, to defend the islands. In the process, characters from both series learn about each other's powers and cultures. Luffy might be intrigued by Ichigo's ability to transform into different forms, and Ichigo could be amazed by Luffy's stretching powers.
One idea could be that Ichigo from 'Bleach' somehow gets transported to the world of 'Inuyasha'. He might meet Inuyasha and they could team up to fight a common enemy, like a powerful demon that has somehow gained the powers of Hollows from 'Bleach'. Their different fighting styles would make for an exciting combination.
One idea could be that the Pokemon trainers gain Shinigami powers. For example, Ash could discover he has the ability to purify Hollows in the Pokemon world, which are like dark or corrupted Pokemon. His Pikachu could also have a unique transformation related to this new power, like having a Zanpakuto - like form.
One idea could be a scenario where Ichigo and Naruto meet in a strange dimension. They initially misunderstand each other but then realize they have a common goal of protecting their respective worlds. They could team up to fight a new threat that somehow has the power to destroy both the Soul Society and the Hidden Leaf Village.
One interesting idea could be the combination of powers. For example, the Soul Reaper's zanpakuto abilities mixed with the unique Semblances in RWBY. Maybe a character from Bleach using their Bankai in the world of RWBY and how that would interact with the Grimm. Another idea might be the character interactions. How would Ichigo get along with Ruby? Their personalities are quite different but they both have a strong sense of justice. It could lead to some really cool dialogue and development.