Chamberlain Sakai Hyobo is an aging leader of the Mochizuki clan who commands the Kōga Team of ninja. He has a burly build and the appearance of an elder, traditionally wearing kimono garments and having spent many years directing his men from within the clan's territory rather than fighting in the field. As the clan chamberlain, his primary responsibility involves investigating the mysterious destruction of Shimoda Village. When only the ninja Kagerō returns alive from an initial reconnaissance, he orders her to continue the investigation alone.

Before the events of the story, Sakai Hyobo is described as a noble leader who guided the Mochizuki clan for decades. However, his men eventually notice a marked change in his behavior: he becomes cold and blunt when issuing orders, and he is seen engaging in frequent sexual encounters with his chambermaids. This shift in personality is later explained when it is revealed that the chamberlain has been killed and impersonated by the villainous Genma Himuro, who used the disguise to destroy the Kōga Team from within.

Near the climax, a figure appearing to be Sakai Hyobo leads a band of Mochizuki warriors to Kashima, apparently responding to a message from Kagerō. To her shock, this figure is actually Genma Himuro in disguise, who reveals that he murdered the real chamberlain days earlier moments before striking down Kagerō. In terms of abilities, Sakai Hyobo likely possessed wisdom befitting a ninja clan leader, but his physical combat skills remain unknown as he never engages in direct fighting within the story.