Ginrei Kuchiki (Byakuya’s grandfather) and Captain-Commander Yamamoto intervene to stop Kōga. During the battle, Kōga tries to call upon Muramasa, but his voice no longer reaches the spirit.
After being framed for the murder of his own comrades, Kōga escapes confinement. Consumed by rage and a desire for revenge, he begins a killing spree, targeting both those who wronged him and innocent bystanders. Bleach Episode 251
As Kōga’s heart darkens, his connection to his Zanpakutō spirit, Muramasa, begins to fail. Despite Muramasa’s attempts to reason with him, Kōga starts to view Muramasa as a mere tool rather than a partner. Kōga tries to call upon Muramasa
Byakuya’s grandfather and the Head of the Kuchiki clan at the time of Kōga’s fall. he begins a killing spree