With the amount of characters bleach has you will be hard pressed to find an utterly unique character, don't worry about it so much. You will be surprised that as long as the Zanapkuto is different the character feels a lot more different than those in the Anime. As far as personality goes make something you would have fun playing and would enjoy. Heck My Captain is like Gin whilst Zume is like Aizen, The Captain commander is....well like the Captain commander. 
A nice little spin in their back story is more than enough to make them independent from other characters so instead of pressuring yourself by thinking of something original just try to have fun with it :)

Edit: Write a mini 1-2 paragraph of a scene involving your character :) that might help you form their personality.