Kyōshin

Kyōshin (鏡心, "Mirror Heart") is an advanced technique derived from  mastery. When it becomes possible for a and their  to become connected to the utmost degree, the blade's own senses are capable of serving as their master's own. In this sense, the two are able to fight as one being.

Overview
Through, a Zanpakutō and its master are able to establish a dialogue with one another. And in mastering the principle of Jinzen, it no longer requires an effort for the two to establish communication for they are at all times connected. In a state where the two become connected with one another, the Zanpakutō serves to fill in the void of their master's limitations. If there is something that they physically are unable to perceive, the Zanpakutō serves to compensate for that weakness; making it possible for their master to anticipate and avoid their adversaries, even while under the influence of suggestion and illusions. However, this is merely the fundamentals of Kyōshin. In establishing a free-flowing dialogue between one another, the Shinigami and Zanpakutō balance one another out and keep each other covered so that there can be no openings to be exploited by the enemy. If their combat patterns, for instance, are being read by their opponent, they are able to substitute their Zanpakutō's own mannerisms to throw off their opponent. The two fight as though they are two minds in a single entity and fight by covering each other's weaknesses in order to become unconquerable.

was able to touch upon this technique only briefly during his battle against the spirit of. While it required a moment to prepare, was able to serve as Ichigo's eyes while he was under Muramasa's hypnosis that seized control of his five senses. In doing so, Ichigo faced the rogue Zanpakutō with his eyes closed, yet was able to not only anticipate every move Muramasa made but managed to counter effectively each and every time.

Notable Users

 * - utilized the principle momentarily against.

Behind the Scenes
This article serves to expand on a concept in the actual Bleach series, albeit found in filler, that was otherwise never actually explained nor truly touched upon.