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.
Well, in a 'dbz bleach crossover fanfiction', you could explore the concept of the Dragon Balls in the Bleach world. Maybe the Soul Society discovers the Dragon Balls and wants to use them for their own purposes. Or perhaps some of the DBZ villains find their way into the Bleach universe and start causing chaos, leading to an alliance between the heroes of both series to stop them. It would be really cool to see how characters like Vegeta and Byakuya would interact with each other, given their very different personalities and fighting styles.
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 a battle between Goku and Superman to determine who is the strongest in the universe. They might start off as rivals but then realize they have more in common than they thought and team up against a greater threat like Darkseid and Frieza combined.
One idea could be that Goku ends up in the world of Aladdin. He might mistake the flying carpet for a new kind of Ki - powered vehicle. And he could use his martial arts skills to help Aladdin fight off Jafar's minions in a really action - packed way.
Another interesting concept is to cross them over with a fantasy world. Saiyans could be in a world full of magic and mythical creatures. Picture Vegeta having to deal with dragons that can talk and cast spells. Their Saiyan pride might get in the way at first when they realize that their brute strength isn't always enough in this new world.
A cool concept could be that Vegeta gets transported to Gotham City. He initially clashes with Batman due to their different methods, but they eventually work together to take down a powerful new enemy that is a threat to both their worlds.
Maybe in the fanfiction, Cell could be re - created in a different form with a mix of other characters' DNA. He could have some of Piccolo's regeneration abilities along with Gohan's hidden power. This would lead to a whole new set of battles and power - level dynamics as the Z - fighters try to figure out how to deal with this new Cell.
One idea could be having the characters from RWBY learn the Ki techniques from DBZ. For example, Ruby could combine her speed with the Instant Transmission technique. This would make her even more formidable in battle.
One idea could be Trunks traveling to an alternate universe where the rules of DBZ are slightly different. For example, the Saiyans never lost their planet but have a different culture. Another could be Trunks teaming up with a character from a different anime in the Dragon Ball Z world to fight a new, powerful enemy. Maybe a character from Naruto who has unique jutsu skills that could combine with Trunks' power in an interesting way.
Well, a really cool concept could be a villain that threatens both the Naruto and DBZ universes. So, characters from both sides have to team up to defeat this powerful foe. Imagine Vegeta and Sasuke having to work together, despite their initial differences. Also, there could be a story where the Dragon Balls are somehow transported to the Naruto world, and Naruto and his friends try to figure out what they are and how to use them.
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.