A cunning warrior who infiltrates Sōsō's forces on a pretense of defection during a major naval battle (based on the Battle of Red Cliffs) and sets the Gi faction's ships on fire. If Kazuto joins the Gi Faction, Kōgai is eventually killed for these actions.
Although she didn't appear much in the first two installments of the anime (she is however seen in the credits of the final episode of Shin Koihime Muso), Kōgai made her official appearance in Shin Koihime Musou Otome Tairan.
She is describe as Go's longest and most trusted adviser.
She played an essential part in getting Sonsaku and Shūyu to stop fighting after the former drank the special drink that the latter purchased in secret for their special occasion. One of her pet peeves is being described or being exemplified as old, once retorting that she is not that old since there are men who turn heads when they see her.