ah, captain aizen of squad 5 of the soul society court guard. he may look pleasant and kind, but underneath he plotting to overthrow the soul society. though the use of his sword the Kyoka Suigetsu's shikai.

which can place anyone who sees it under a state of absolute hypnosis, after which aizen can make them see whatever he wants. the hypnosis is unbreakable ,even if the target is aware that they are hypoitzed. such a scary power that can't be overwritten, his bio is on wikipedia.org.