Moka and Byakuya would be quite unexpected. Moka is a vampire in Yokai Academy with her own set of powers and a somewhat ditzy personality. Byakuya, on the other hand, is a stoic and powerful Soul Reaper captain. Their interactions would be full of contrasts, with Moka's bubbliness clashing against Byakuya's cold demeanor, but also potentially leading to some unique character development for both of them.
Another unexpected pairing could be Gin and Kurumu. Gin is a rather sly and mysterious character in Bleach, while Kurumu is a succubus in Yokai Academy. Their meeting could be filled with all sorts of mischief. Gin might be interested in Kurumu's powers and how he can use them to his advantage, while Kurumu could be intrigued by Gin's enigma and try to get closer to him, creating a complex and comical relationship.
Tsukune and Rukia could be an unexpected pairing. Tsukune is a normal human in a world of yokai, while Rukia is a Soul Reaper from the world of Bleach. Their different backgrounds and powers could lead to an interesting dynamic. Rukia could teach Tsukune some combat skills, and Tsukune could show Rukia the more light - hearted side of the yokai world.
Urahara Kisuke and the headmaster of Youkai Academy could be an unexpected but fascinating pairing. Urahara is full of secrets and has a deep knowledge of the spiritual world. The headmaster of the academy also has a lot of knowledge about Youkai. They could either be at odds, each thinking the other is a threat to their world, or they could end up working together to solve a problem that affects both the Bleach world and the Youkai Academy world.
Definitely Ichigo and Ben. Ichigo has his strong sense of justice and his powerful Hollow - Soul Reaper abilities. Ben, on the other hand, has the Omnitrix with all its different alien forms. They would make an interesting duo as they could learn from each other's fighting styles and powers. Ben could learn about the spiritual aspect of Ichigo's powers, and Ichigo could be amazed by the physical transformations Ben can do.
Yang and Kenpachi would be a wild and exciting pairing. Yang is all about brute strength and has a bit of a hot - headed nature. Kenpachi is the same, always looking for a good fight. They could have some epic battles together, or team up and be an unstoppable force. Also, Blake and Urahara could be an interesting pair. Blake is stealthy and intelligent, and Urahara is a mastermind with all kinds of tricks up his sleeve. They could scheme together to solve the problems that come up in the crossover world.
Naruto and Rukia could be an interesting pairing. Naruto's exuberant and positive personality could contrast with Rukia's more reserved and serious nature. They could learn a lot from each other. For example, Naruto could teach Rukia about the importance of never giving up and believing in oneself, while Rukia could show Naruto the more disciplined way of the Soul Reapers.
I think Uryu and Weiss could be a fascinating pairing. Uryu is the Quincy with his pride in his heritage, and Weiss is the Schnee heiress with her own sense of family pride. They could have some intense debates about their families and legacies. At the same time, they could learn from each other's combat styles. Uryu could show Weiss how to be more adaptable in battle, while Weiss could teach Uryu about the importance of elegance in combat.
One interesting plot twist could be a character from Bleach accidentally getting sent to Yokai Academy. Maybe Ichigo ends up there and is mistaken for a new yokai student. His reiatsu could be misinterpreted as some kind of strange yokai power, leading to all sorts of chaos as he tries to figure out how to get back home while also dealing with the unique challenges of the academy.
I think Haru from Free! and Kuroko from Kuroko no Basuke would be an unexpected pairing. Haru is so focused on swimming and his own world of water, while Kuroko is all about basketball and his quiet, yet strategic play. But if they were paired together, Kuroko's calm and calculated nature might complement Haru's single - minded focus. They could learn from each other's dedication to their respective sports.
I think an unexpected pairing would be Thor and Levi. Thor is this powerful god from Asgard, used to grand battles and magic, while Levi is a very skilled and no - nonsense human from the Attack on Titan world. They would probably clash at first due to their different personalities, but then learn to respect each other's skills.
Hermione Granger and Rukia Kuchiki could make a great pairing. Hermione is extremely intelligent and well - versed in magic theory. Rukia, on the other hand, has a deep understanding of the spiritual world. They could collaborate on researching a strange phenomenon that is occurring between the two worlds, like a merging of certain spells and Soul Reaper techniques. Their different personalities would also create some interesting interactions, with Hermione being more outspoken and Rukia more reserved.
Ichigo and Sailor Moon herself would be an interesting pairing. Ichigo is a strong - willed fighter in Bleach, and Sailor Moon has a pure heart and great power. Their personalities are quite different, but they both have a strong sense of justice. They could learn a lot from each other, like Ichigo could teach Sailor Moon some combat skills, and Sailor Moon could show Ichigo the power of love and friendship in fighting evil.