As to how Bane was banished. He got possessed by a being that caused him to attack other knights on his countrys' side. He was a Kirin knight working with other magically enhanced beings to help stop some chaotic beings. After a few knights knocked him out cold, making the being let go of his possession, he was banished and was drained/put under a spell to restrict a good chunk of his magical abilities. This didn't make him lose his beast form, but he's just in general more restricted on other magical abilities. Like he were in beast mode he would only be able to glide for a couple of seconds, and be exhausted. Unlike other Kirins. Thus making the form more like a on the ground travel form instead of a more powerful form. Also he intends on kicking that beings' ass, one day

Also banishment isn't a merciful punishment among Kirins, since leaving their own country can be really troublesome and is really dangerous since they live where most mystical beings live. Since the civilized/towns/villages/etc are normally protected by a magical force field to keep other magical threats out (like most demons and Kitsunes), being banished means you're treated as a threat and you are not well able to tap into some abilities making it very easy for a more powerful threat to kill you off. That and Kirins prefer to live amongst themselves, so if they do manage to get out of their country alive and into another city, they may have a hard time getting used to not having most abilities and adapting with other species.