Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
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.
A good way to create compelling character interactions is to play on the differences in their powers. Take Lucy from Fairy Tail and Uryu from Bleach. Lucy uses her celestial spirits, while Uryu has his Quincy powers. If they were to meet, they could initially be curious about each other's powers. Lucy might be amazed at the precision and control Uryu has over his arrows, while Uryu could be intrigued by the concept of celestial spirits. This curiosity could lead to them trying to learn from each other, or even having a friendly competition to see whose power is more effective in a certain situation. Through these interactions, their characters can grow and a deeper relationship can be formed.
One idea could be a tournament where characters from Bleach and Fairy Tail compete. For example, Ichigo from Bleach could face off against Natsu from Fairy Tail in a battle of strength and sword skills versus fire - based magic. Another plot could involve a common enemy that forces the two groups to team up. They start off distrusting each other but gradually learn to work together. Maybe a powerful dark force is threatening both their worlds and they have to combine their powers to defeat it.