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.
For 'bleach crossover fanfiction', consider a crossover with Attack on Titan. The Titans could be a new threat in the Bleach world, and the Survey Corps could team up with the Soul Reapers. This would create a lot of action - packed scenes as the two groups with different fighting styles and abilities join forces.
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.
One idea could be that Sasuke somehow ends up in the Bleach universe and teams up with Ichigo. They could face off against a common enemy that has powers related to both the Sharingan and the Zanpakuto. For example, a villain who can manipulate souls like in Bleach but also has the ability to copy techniques like the Sharingan.
One idea could be to have Goku from DBZ end up in the Bleach universe and learn about soul reapers. He might mistake them for a new type of fighter and try to spar with them. Another could be a fusion of the power systems, like Ichigo getting the ability to go Super Saiyan on top of his existing powers.
A cool concept would be to combine the magic systems. So, the Soul Reapers' Kidou could be related to Fairy Tail magic in some way. For example, a Soul Reaper could teach some of the Fairy Tail mages how to use Kidou for a special mission against a common enemy that has the ability to disrupt both the Soul Society and the Fairy Tail world.
Another idea is to have the Death Eaters somehow get access to Hollow powers. This would create a whole new level of threat in the Harry Potter universe. The characters from Bleach could then be called in to help the Order of the Phoenix deal with this new threat. Harry Potter might learn some skills from Ichigo about combat and vice versa.
A possible plot could involve the Hollows from Bleach somehow making their way into the Inuyasha universe. Inuyasha and his friends would have to team up with Ichigo and the Soul Reapers to fight them. This would create a really interesting dynamic as the different fighting styles and powers collide. The Hollows might also target the demons in Inuyasha's world, seeing them as a new source of power or prey.
A possible plot is a tournament - style crossover. Characters from both Naruto and Bleach are invited to a special tournament in a neutral dimension. This would lead to some really exciting match - ups like Sasuke vs. Byakuya or Naruto vs. Renji. They would fight not just for victory but also to prove the superiority of their own world's fighting styles. Along the way, they might learn from each other and form unexpected alliances.