Erza and Byakuya would be an interesting pair. Erza's leadership and unwavering determination in Fairy Tail, and Byakuya's noble and stoic nature in Bleach. They might initially have a bit of a standoff due to their pride, but as they face challenges together, they would come to understand each other's values and form a mutual respect.
One interesting plot could be the characters from Fairy Tail and Bleach teaming up to fight a common enemy that threatens both their worlds. For example, a powerful dark mage from Fairy Tail's world teams up with a rogue Hollow from Bleach, and the heroes have to combine their unique powers to stop them. The Fairy Tail mages could use their magic, like Natsu's fire magic, while the Soul Reapers use their Zanpakuto abilities.
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.
The most interesting aspect is seeing the characters interact. For instance, seeing how the stoic characters from Bleach react to the more exuberant ones in Fairy Tail can be really entertaining.
One interesting plot point is the clash of magic systems. In 'bleach and fairy tail crossover fanfiction', you often see how the spiritual powers from Bleach interact with the magic of Fairy Tail. For example, a shinigami's zanpakuto abilities against a Fairy Tail wizard's elemental magic can create some really intense battle scenes.
One idea could be that Ichigo from Bleach somehow ends up in the Fairy Tail world. He could join forces with Natsu and the gang to fight a common enemy. Maybe an Arrancar has escaped to the Fairy Tail universe and is causing chaos, and Ichigo's skills as a Soul Reaper are needed to stop it.
One interesting crossover idea could be a battle tournament where characters from both Bleach and Fairy Tail participate. For example, Ichigo from Bleach could face off against Natsu from Fairy Tail. Their different fighting styles, with Ichigo's zanpakuto and Natsu's dragon slayer magic, would make for an exciting showdown. Another idea could be a team - up scenario. Maybe some of the Soul Reapers and Fairy Tail mages have to work together to defeat a common, powerful enemy. This would allow for interactions between characters who have different powers and personalities, like Rukia and Lucy. They could learn from each other's magic systems and grow as characters during the adventure.
Natsu and Asta would definitely have an interesting interaction. Natsu is all about his dragon - slayer magic and has a fiery personality. Asta, on the other hand, has no magic but his anti - magic swords make him a formidable fighter. They would probably start off challenging each other, but then realize they can learn from one another. Natsu could teach Asta about the power of raw magic, while Asta could show Natsu the importance of determination without relying on traditional magic.
The fire - based abilities of Natsu from Fairy Tail and the ice - based abilities of Hitsugaya from Bleach could create some really cool interactions. Natsu's heat might be able to counteract Hitsugaya's ice in an interesting way, like when they fight together against a powerful foe. Their different combat styles, with Natsu's more brute - force approach and Hitsugaya's more calculated and precise strikes, could also make for an exciting combination.
Itachi and Gray could also have great interactions. Gray is a cool - headed ice mage. When he meets Itachi, they could compare their elemental powers (Itachi's fire - based jutsu and Gray's ice magic). They might also bond over their somewhat stoic personalities and the secrets they both carry.
Another interesting interaction would be between Deadpool and Gray. Gray is cool - headed (pun intended) and has his own unique fighting style with ice - make magic. Deadpool's chaotic fighting style would contrast greatly with Gray's. They could start off as rivals, with Deadpool constantly taunting Gray about his stripping habit, but then as they face a common enemy, they would have to learn to work together. This would lead to some great character development and some hilarious exchanges as Deadpool tries to understand Gray's magic and Gray tries to tolerate Deadpool's antics.