Kyou Kai was born into the legendary Clan Shiyuu and raised among the isolated Kyou Tribe alongside her adopted sisters Kyou Shou, Kyou Shiki, and Kyou Rei. Trained from childhood under the clan's strict traditions as a deadly warrior, she was recognized as the tribe's most gifted fighter. She and Kyou Shou were selected for the ritual to determine the next Shiyuu—the clan's strongest assassin. However, Shou drugged Kyou Kai to prevent her participation and was subsequently murdered by rival candidate Yuu Ren through deceit. Discovering Shou's severed head, Kyou Kai slaughtered the attending elders in grief and abandoned the clan, vowing revenge against Yuu Ren. She enlisted as an infantry soldier in the Qin military during the Keiyou Campaign. Assigned to Taku Kei's squad within Duke Hyou's army, she initially displayed aloofness, rarely speaking and showing disinterest in social interactions. Her first notable action occurred during the Battle at Dakan Plains, where she devised a strategy using piled corpses to counter enemy war chariots. She saved comrade Bi Hei from attackers, showcasing inhuman swordsmanship by bisecting five soldiers in one stroke, marking her first connection with future comrades including Ri Shin. Leaving the military temporarily to pursue vengeance, she infiltrated Qin's royal palace during an assassination plot against King Ei Sei. Confronting Shin, who defended the king, led to a temporary truce against common enemies. Her previously concealed gender was discovered by Ka Ryo Ten. After defeating Yuu Ren in a duel, she fulfilled her revenge and returned to the Hi Shin Unit with a renewed purpose: to become a Great General of Qin and honor Kyou Shou's memory. Her extraordinary combat abilities stem from Shiyuu training. She manipulates qigong to enhance her physical prowess, achieving superhuman strength, speed, and reflexes. Her signature "Priestess Dance" temporarily amplifies her capabilities to near-unrivaled levels, though it exacts severe physical recoil. She wields the sword Ryoku Sui with lethal precision, mastering techniques like the "Mist Technique" (rapid multi-angle slashes) and "Dancing Step" (movement imperceptible to the human eye). Her tactical acumen initially served the Hi Shin Unit as primary strategist before Ka Ryo Ten assumed the role. Kyou Kai's personality evolved from detached and taciturn to increasingly integrated within the unit. Initially expressing disdain for social norms and prioritizing survival, stating "I can't die in a place like this," she developed loyalty, protecting comrades and openly acknowledging emotions. Her relationship with Shin transformed from indifference to deep mutual respect and romantic love; she confessed her feelings, declared intent to bear his children, and sacrificed half her lifespan using forbidden medical qigong to save him from mortal injury. As a commander, she rose through Qin's ranks, eventually leading the 5,000-strong Kyou Kai Army while remaining affiliated with the Hi Shin Unit. She participated in pivotal conflicts including the Battle of Bayou (where she first sensed and fought the Bushin Hou Ken), the Coalition Invasion, and the Western Zhao Invasion. Her reputation as a "monster" on the battlefield spread across states, with strategist Ri Boku noting she requires double the soldiers to challenge. Her current goals include responding to Shin's marriage proposal and achieving Great General status. Kyou Kai's appearance remains consistent: black hair tied with a white ribbon, pale skin, and green eyes. She wears the Kyou Tribe's signature attire—a red robe with decorated sleeves, white headband bearing red tribal marks, and neck scarf—never adopting standard military armor. She carries Ryoku Sui on her back during campaigns and daily life.