Kōga Kuchiki

is a rogue Shinigami who once revolted against the Seireitei.

History
Sometime before the main storyline, Kōga revolted against the Seireitei. He used his Zanpakutō, Muramasa, to make other Zanpakutō spirits abandon their wielders and attack them. The Shinigami were eventually able to seal Kōga away. Kōga's revolt was never recorded in the Soul Society's history.

Synopsis
Kōga was sealed away, but his Zanpakutō Muramasa eventually resurfaces and begins to initiate a Zanpakutō rebellion. When Ichigo Kurosaki encounters Muramasa, he states that he already killed his master. However, after Muramasa gains control over Ryūjin Jakka, Genryūsai Shigekuni Yamamoto reveals that Muramasa is planning to break Kōga's seal. He also states that Muramasa is heading to Karakura Town, where Kōga was sealed.

Muramasa eventually arrives at the location where Kōga was sealed, but he comes into conflict with Orihime Inoue, Uryū Ishida, Yasutora Sado, and Rukia Kuchiki. He ultimately succeeds breaking Kōga's seal. As Ichigo arrives to stop him, Kōga begins to awaken.

Zanpakutō

 * Kōga's Zanpakutō takes the form of a standard wakizashi with a purple hilt-wrapping and a guard in a shape similar to the Kidō Corps' emblem, consisting of a circle with a triangle-like shape in the center and three points protruding from the edges evenly spaced apart.


 * Shikai: The form and release command is unknown.
 * Shikai Special Ability: Muramasa can break into the inner world of targets and forces them to bend to the user's will. It can cause a Zanpakutō's spirit to abandon its master and attack them.
 * Bankai: Not Yet Achieved.
 * Bankai: Not Yet Achieved.