Quincies in Bleach are the polar opposite of the Shinigami. Despite the two of them being important spiritual beings required to keep the balance between all three realms, Quincy have the ability to completely wipe out Hollows from existence. This ability may be useful in some situations, but 200 years ago, when the Quincy began to overhunt Hollows, it tipped the balance between the realms. This led to the Shinigami-Quincy War in Bleach, which resulted in most of the Quincy being eliminated to keep the peace.