She and her sister Shou were trained from a young age to become deadly warriors and both hail from the Kyou tribe of the Shiyuu clan. She cared deeply for her sister and said she would not feel bad dying at her hands for the Shiyuu ritual. She woke up late and found that Shou had used some incense to put her into deep sleep the night before. Racing to the ritual site, she arrives to find the bodies of potential Shiyuu all over the ground and looks for her sister's corpse. Clutching her severed head, Kyou Kai mourns the loss of her sister, asking her granny what happened. The elder informs her that Shou was targeted from the start by all the other candidates and says that it was allowed because both her and Shou were far above the rest in terms of ability. The elders gather and tell her to commit suicide as the victor has already been decided and she is nothing but a walking corpse, instead, she kills all those present.
After leaving her clan, she met Shin during Duke Hyou's campaign against the state of Wei while he was looking for a Go unit to join in the army. They are eventually assigned to Taku Kei's squad and when the members introduce themselves, they assume Kyou Kai is a mute until she speaks saying that she dislikes talking. During the battle against Kyuu Gen's forces, she speaks up, saying she has a plan to deal with the Wei war chariots. The plan was to pile up Qin corpses in the form of a rampart to interfere with the enemy's mobility. Other squads quickly mimic this tactic and gain a fighting chance against the Wei. She tells Shin that it is his chance to attack and advises him on how to defeat the chariots by targeting the wheels instead of the riders. When Baku Koshin orders them to charge the hill, she talks about the difficulty of the task and the situation they will face. Shin notices that she's gotten more talkative since the chariots appeared and asks why the change to which she replies that she can't die here. She saves Bi Hei from being killed, cutting 5 of his attackers in half and shocking all present. Holding her position with the 6 infantry who climbed the hill, she cut through Wei troops, displaying speed and agility before she ran out of breath.
After the campaign, she drops by Shin's home to warn him not to interfere with what goes on at the royal palace, stating that he will lose his life if he goes. She is present during a secret meeting, along with other assassins, at the home of Mister Shi who was the former advisor to Ketsu Shi. Her appearance shocks all those present as they failed to detect her presence and the three assassins from Shukyou Clan knelt before her upon knowing she was from Clan Shiyuu. Shi tells them that their goal is to assassinate the Qin King in the dead of night. Quietly infiltrating the palace, she stumbles upon members of Clan Kakuriki who had captured Ka Ryo Ten. When she asks them to hand Ten over, they attack her and are all subsequently killed in the process.
She and Clan Shukyou find the king, Ten and Shin trapped in a chamber within the palace and Shin cuts down one of the Shukyou men who charge at them. She walks forward to fight Shin and tells him that she is an assassin. Dodging his strikes, she easily attacks Shin on various parts of his body but he refuses to give up. Not understanding why, she asks him and he says that he's defending the king because they are comrades. Clan Gouma interrupts their fight and Shin calls for a truce with her so that they can defeat the intruders. She tells Shin to stall the assassins for 30 seconds so she can get her breath back and takes a seated stance. After gaining enough breath for one round, Kyou Kai begins her martial dance and annihilates most of the Clan Gouma members present before passing out from exhaustion.
She is tied up on a bed by Ten but easily escapes her bonds and helps calm Shin's fever down before leaving through the window. Ten waits below the window and confronts her, saying she knows that Kyou Kai is a girl. She asks the assassin to teach her the techniques of the Shiyuu before they are interrupted by the leader of Clan Shukyou. He praises her swordplay and offers assistance in her endeavors but she declines, calling the bonds between their two clans a thing of the past. After he departs, she tells Ten that it is impossible to train her as the environment they were born and raised in are far too different. As Ten's constitution is not suited for learning the Shiyuu techniques.
Kyoukai leads Ten to some connections that could train her in becoming a strategist. After passing Ten's message to Shin, she is invited into his home where they discuss about Ten's choice and she sleeps over before leaving in the morning.
Kyoukai runs into Heki as he and his unit head to the impending Zhao conflict, she states that her sword is irritated. She returns to the Hi Shin Unit before they head out from Kanyou as her "target" has moved from Wei to Zhao and spars with Shin as the army marches to Baou. She talks about the origin of the Priestess Dance and mentions the existence of the Bushin. During the Battle of Bayou when the Hi Shin unit is sent after Zhao General Fuu Ki's head, she kills all the posted Zhao scouts, allowing them to get closer to the general and his guards. After killing an enemy captain, she rides along with Shin on his horse as they head for Fuuki.
As the Qin army rested from following the retreating Zhao, she sensed Hou Ken's presence moving about in the camp. She attacks Houken after Shin does, asking who he is, then hears him say he is the Bunshin. She senses him giving off the sensation of a Shiyuu utilizing her chi and remembers the clan teachings to never approach the Bushin. After engaging in a pincer move against the daunting man, Kyoukai is shocked when he turns on Shin, knocking him out cold. He attacks her as well but she manages to dodge and begins the Priestess Dance, aiming for a short fight. Diving deeper into the technique, Kyou Kai begins to gain the upper hand as she dodges and cuts Houken several times before aiming for his neck when the dance had reached its deepest depth. He blocks this and another attack, saying that the ability to predict an opponent's movements is not hers alone then she begins to feel the aftereffects of using the Priestess Dance. Sweating profusely and going pale, she feels her body get heavy and throws up as the recoil from her technique catches up to her. Then 500 Zhao arrive under the command of Man Goku. Shin then rises and orders his to fall back and regroup, while Shin and Kyou Kai cover them. Instead the Kan Ou Army shows up and attacks the Zhao. During the chaos, everyone slowly find their way back to Shin. When Shin wants them to fight Hou Ken, Suu Gen tells him that he understands his feelings, but he should take a minute to calm down and think it through. And they cannot defeat him by blindly charging like that. If they were to fail in their gambit after entering the middle of that, there’s no doubt their unit will be annihilated. Shin reminds him of when they took Fuuki’s head, and how many of their men gave up their lives so they could take it. And how their centre and right armies sacrificed thousands, and what they had to show for it. That is what war is. But right now, the Zhao Commander-in-Chief was right in front of them. But he agrees with him, so he asks if anyone wants to pull out. Shin has everyone apart from him and Seki’s squad split into three groups. Kyou Kai knew it was useless to stop Shin. But she told him, her breath doesn't seem to be coming back, and not to rely on her to do anything. And he tells he wasn't planning to. The men then, take position surrounding Houken from three directions. Gathering as many of the nearby spears as possible. Then hold position and wait for the signal. On Seki’s whistle signal, all three groups made a beeline for Houken. Then threw spears at him from all three directions. He deflected all of them, but while he deflected them Shin snuck up on him from behind. He still noticed him, but Shin knew he would and dodged the swing.When he goes to cut him, Shin knew that Houken would still notice and go for another swing so he dodged it and slashed him. But it didn’t work. Before he could make another move he is hit by the backend of his glaive. And before Houken can kill Shin, Kyou Kai protects him, and is blow away. Then as he goes to kill Shin, he is protected by the Bi brothers and Taku. The Hi Shin unit comes to their aid before retreating as Mangoku chases after them. Den Yuu then splits off from the main group carrying Kyou Kai to safety.
The next morning, they find the others after hearing Seki’s whistle. Kyou Kai is carried by Denyuu and Bi Hei by Chu Tetsu. He explains to them that Bi Hei used himself as bait to lure away the trackers. That how their group, which was chasing after Shin, ran into Bi Hei who was on the verge of death. They then ended up be caught by Zhao soldiers, but Kyou Kai pushed herself to the limit and helped them get away. He then puts a now conscious Kyou Kai down, because she says she can walk. Bi Hei wakes up and tells everyone Shin will be fine in Bi Tou’s hands. He tells them to send out search teams, and he has a pretty good idea what direction they’re in. But Seki tells them Shin has returned, carrying Bi Tou. As everyone is relieved of their return, Shin tells Hei he’s sorry. And lays a lifeless Bi Tou down.
When Shin asks Kyou Kai who is stronger between Houken and Ou Ki. She tells him Houken and gets angry comments from the unit members.
While discussing battle strategies, Do Mon informs them that the battle will be drawing near. That night Kyou Kai informs Shin after the war she will leave the Hi Shin Unit, to go avenge her sister. And when she’s done she will come back, so she can move forward with them.
On the day of the battle they find out Ren Pa is not the Commander-in-Chief, so he won't be limited to staying in headquarters.
Later Shin is informed the enemy is targeting newly formed 1000-Man Units. With the 1st wave suffering heavy damage the 2nd is called in. Unlike the other the Hi Shin Unit was doing well by fighting as separate bodies. But under the rule that “no matter what time it is, and no matter what enemy you happen to be fighting the moment there’s a signal, we will all charge the target marked by Captain Shin and strike them as 1000 men in unison”-Sosui
When the Wei 2nd wave appears they set off smoke bombs to have the 1st army retreat. The Wei then begin to attack the Qin with arrows from outside of the smoke. No matter where they went the arrows kept coming, Kyou Kai figured out the Wei were transmitting their position using sound. But it is useless to kill the sound teams because more would just take their place. As they are about the pull out of the smoke the Wei send out their chariots. Kyou Kai comes up with a plan to make noise themselves to confuse the enemy. En comments saying that there has been a low ringing sound since the battle, to which Kyou Kai replies it must be the enemy command squad. So if they then figure out the place that’s giving off the noise they find the location of the enemy command group. Shin has the Seki Squad figure out where the noise was coming from. They take the Cavalry leaving the Infantry with En. When they reach the command group they are caught in a trap. While Shin is leading the charge from the front he gives everyone the strength to go on. When the enemy starts to aim for Shin, Sosui sends the Retsu Brothers to guard him. As they close in on the enemy infantry they are knocked off their horses by an anti-cavalry picket trap, which was hidden underground. Thanks to this trap, the Hi Shin Unit’s Vanguard was nearly completely destroyed, leaving only a handful of survivors. Being cut off from their comrades, Shin and a dozen other members were trapped by 800 Wei soldiers. As they were being slaughtered by the Wei, the smoke began to come to the rear of them. Then the Gyoku Hou Unit suddenly appeared from amidst the smoke. They began to head for Gen Bou. Then the rest of the Hi Shin Unit’s cavalry shows up having imitated the Gyoku Hou and came be stepping on top of corpses. They then begin to chase after the Gyoku Hou and claim Gen Bou head for themselves. When they catch up to the Gyoku Hou unit, Shin notices the injuries on Ouhon. He raises their morale, by insulting them. As they are about to reach Genbou he has all his forces retreat. As they are retreating Shin throws a spear at Genbou, which only hit the top of his seat. Sosui tells Shin they did enough by causing the Wei to retreat, but Shin says that they were completely crushed by Genbou.
The Mou Gou Army which had suffered a devastating loss in the opening battle set up Shin and Ouhon as the heroes of the battle in an effort to preserve morale.
At nightfall, Mou Ten informs Shin that Genbou was killed by Kan Ki. Then he invites Shin to Ou Hon’s tent. Mou Ten has their three units fight together to strike down Rin Ko. The next day the Gaku Ka Unit switches back to and independent entity and heads out, leaving 200 men to cover their spot. They aim for Rinko’s command, but their target isn't Rinko rather his own personal soldiers. When Mouten gave the signal both the Gyoku Hou Unit and Hi Shin Unit rush out. Thanks to the Gaku Ka’s first engagement, all the Wei soldiers were on guard thinking that it was some sort of concerted attack with other units. But it was only the Gaku Ka unit all by themselves grabbing the enemy’s attention. So there was little to no obstructions for the Hi Shin and Gyoku Hou. When they started to close in on the enemy command, the Gaku Ka opened a path by leading the Wei soldiers away with them. Leaving only Rin Ko’s remaining soldiers. When So Sui takes a hit from one of Rinko soldiers and kills him, Kyou Kai goes back for him saying the Hi Shin Unit has need of him in the future. Then Shin heads for Rinko. When Shin and Ouhon fight him, he tries to finish off Ouhon, who is the more troublesome one, but is interrupted by Shin. Rinko thinking he can easily defeat Shin is surprised when he blows him away, and is capable of keeping up with him. Rinko states Shin is capable of bringing out more power the stronger his opponent is. As Ouhon and Shin rush Rinko he is able to fend off both their attacks. Shin states that, “Being able to wound even general Ou Ki wasn’t just some idle rumor.” Rinko claims that they don’t understand what its like to go up against General Ouki. Shin tells him that Ouhon from the same family as Ouki, and he’s the one that inherited General Ou Ki's Glaive. And he’s the man who inherited his dying will, and the man who will surpass all other generals and become the strongest general in history. When he says that after he slays him Renpa is next, Rinko slashes Shin across the forehead, saying to Shin not to get ahead of himself because today is the last day of his life. As they are fighting Rinko Deals heavy blows to Shin. Shin realizes why all the Great Generals he’s seen are so strong isn’t simply because of the number of battles they’ve been in, they managed to overcome it right in the heat of battle over and over again. Shin then begins to surpass his limits, he uses his “Jump Attack” and breaks Rinko’s horse and cut off two fingers on his left hand. The Hi Shin and Gyoku Hou then pull out, but are surrounded. Then Ban You comes and has secured an escape route.
That night as Kyou Kai tends to Shin’s wounds, she gives him a secret medicine passed down in her village. She uses her small supply on Shin ignoring her own wounds. The Next morning Shin is up and feeling fine. Kyou Kai claims half was due to the medicine and the other half was due to his absurd healing strength. Then, Ryuu Sen notices that the spot they left Kyou Kai and the other injured men is empty. A dying Wei soldier mockingly tells them that their reserve unit of 500 men from Kai Shi Bou’s personal retinue posted to the side of Rinko’s main force, broke through their weakened areas, when their attention was turned. So the comrades they left have been killed by know. They then rush over to the area. They find a mountain of corpses. After a while they find an exhausted Kyou Kai standing over a large amount of large enemy corpses.
Just when Shin arrives in front of Kyou Kai, he then dismount and catches Kyou Kai onto his arms. Then because of tears in her clothing, the unit figures out Kyou Kai is really a women. Then Den Yuu reminds everyone of all the time Kyou Kai had saved them, and it doesn't matter that she’s a women. And for a young girl like her to be so skill with a sword, then going as far as to take to the battleground while disguised as a man, she must be carrying a great burden or task on her shoulders. Shin responds by saying its the opposite, because Kyou Kai is actually “empty.” And she is on a journey to avenge her sister. Then she finally started to look past her revenge, for a place where she can return to after its done, and that place was the Hi Shin Unit. So they decide to treat her the same as before, and the fact that she’s a woman might someday reach the enemy, and once that happens she would be targeted specifically for that reason. So they made a pact to use what little strength they had to protect Kyou Kai together.
The Hi Shin Unit was allowed to return home as a small gesture of reward by General Mougou. On the journey home Kyou Kai decides to leave before Shin wakes up. As she is leaving she is caught in a trap set by Shin, as punishment for trying to sneak off by herself. Then Shin tells her that no matter how much distance is between them, they’ll be supporting her from behind. She then proceeds as Shin was thrown into the hole.
Kyou Kai is seen traveling through Zhao on her quest to find her nemesis. She is worried about the Unit and wants to return however she has faith in them that they will survive somehow. She gets angry at a citizen who was giving off false information as fact. He stated how Qin had already been wiped out and the war was over, only to be told that was a false rumor. Upon discovering what he said was a lie she threw a hot bowl of food at him in anger. She is shown meditating and thinking about the safety of Shin and the Hi Shin unit.
Kyou Kai finally met up with Kyou Mei, the leader of a group of informants that serve the Kyou tribe keeping them informed on changes in the outside world, in the village of Roubi. Kyou Mei informed Kyou Kai that she was the first person from their tribe she has met in 17yrs since she escaped. Kyou Kai was curious as why she is still alive, since by the laws of the village she should have been hunted and killed a long time ago. Mei replied that many pursuers were sent after her but she kept shaking them of, until she was offered to become an informant. Kyou Mei then pointed to the mountain in the distance called Mount Rou, the current base of operations for the Shiyuu Yuu Ren.
After running through the woods Kyou Kai encountered Yuu Ren standing on the edge of a hill looking down at her. Yuu Ren revealed she already knew she was coming for her and the rumors of her location were spread on purpose to lure her into a trap. Kyou Kai found herself surrounded by over 20 member of the Yuu tribe, who, on Ren's command, started a coordinated attack on Kyou Kai, performing their priestess' dance.
Kai warned all members of the Yuu tribe, that her only enemy was Yuu Ren and anyone that got in her way would be shown no mercy. As the warning didn't work, she killed almost all of them, with close to no effort. Since the more formidable foes were left standing, Kyou Kai went into her dance and started a massacre of the Yuu tribe, even forcing some of them out of their dance. While Kyou Kai was calculating her current breath, and strategy Yuu Ren made her move.
Having survived the Shiyuu ritual, Yuu Ren had managed to completely suppress her own sentiments and feelings, obtaining the effect of the pristess' dance without actually having to perform the dance. By doing this, her power was far greater than Kyou Kai's and she managed to overwhelm her in the fight and beat her to a pulp.
Kyou Kai, thinking of her comrades in the Hi Shin Unit, decided she would not give up her life so easily, and so she made a bold move. She broke the Hakuryuu taboo, entering a state so deep, that it was almost impossible for her to return to the conscious world. Moving instinctively, Kyou Kai was extremely fast and unpredictable for Yuu Ren to trace. After a one sided battle with Kyou Kai having the upper hand, Yuu Ren was brought down by the numerous injuries inflicted by Kyou Kai's relentless attacks and was ultimately stabbed through the heart from behind.
Yuu Ren can't believe she lost to someone who didn't even take part in the ritual. Kyou Kai informs her it was by chance she met a group that kept her tied to the outside. Yuu Ren says that impossible as the dance is suppose to sever all those connections. She thinks for that reason the Shiyuu and stops and ponder the implications behind this information. Yuu Ren then says a power like Kyou Kai's should not exist as it denies everything the dance and Shiyuu stands for. She warns her the next Shiyuu will definately come to kill her, Kai just states that's fine, "Let them come I definitely won't lose." Yuu Ren glares as her one final time calling her a little girl and dies. She then ask Kyou Mei to hide Yuu Ren's body and let it appear that she was unsuccessful in killing Yuu Ren. People will assume Yuu Ren's whereabout are unknown but alive somewhere, and it will also prevent the clan from immediately holding another Ritual. This was to protect the two young girls Kyou Shiki and Kyou Rei from Kyou tribe who has relationship similar to Kai and Shou. She also tells Mei to inform granny she got her revenge and she will no longer return to the village.
Kyou Kai begins her return journey after being gone for 392 days to the Hi Shin Unit where she can now move forward with them. Everyone is happy and excited at her return, Shin then ask her if it is finished to which she replies yes. Shin then says good, now you can move forward with us. Upon her return the unit gain more power and flexibility on the battlefield and their overall performance rose to even greater heights. With her keen command on the battlefield Kyou Kai would rack up many achievements eventually her feats would cast a shadow on Shin and the rest of the unit. She informs Shin that she made a vow of two goals, 1 she will also aim to become a great general. Kai feels her sister Shou would have done the same, and if you choose a life of war then you should aim for the pinnacle of that field a Great General. Ten states it sounds more realistic when Kai says it than Shin and everyone agrees. Shin then ask what her second goal is to which she replies to have Shin's child. Everyone is in complete shock and Ten ask her if she knows how babies are made. After confirming that she really doesn't know,Ten informs her of what needs happen which makes her avoid Shin for a while. Later Kyou Kai and Shin have a duel while discussing the current military strength of Qin and what it would take to conquer all of China.
As the Subjugation Force led by General Heki is attacked by both the Qin and Zhao armies, the Hi Shin unit appears. It is revealed that they are now a 5000 man unit, with Shin a 4000-Man Commander, and Kyou Kai a 1000-Man Commander. Arriving at the battle, the Hi Shin unit quickly manages to defend the Subjugative Force and attack the enemies. They also use a tactic devised by Kyou Kai, Herculean Strength (Gouriki) where 10 men form up with shields and toughen up, becoming an immobile block that nothing can pass through. Kyou Kai later along with Shin is informed by Heki that Sei Kyou has been caught in a conspiracy against him. Kyou Kai manages to search and find Sei Kyou and Rui who are running away from the rebel forces.
State Called to aid General Tou, the Hi Shin unit was tasked with breaking through one of three fronts, annihilating the Wei’s reserve units, and –along with the Roku O Mi Army and Gyoku Hou unit- simultaneously assaulting enemy headquarters on the afternoon of the third day.
Everything went well until commander Jun Sou of Gai Mou Army, kidnapped Ten in the heat of battle. Unable to save her friend, she instead captures Jun at Ten's direction. During the debriefing that follows she blames herself for letting Ten get taken away, but then goes on to pose a solution, noting that Jun could be used for a prisoner exchange.
After Shin was promoted to 5000-Man Commander. Kyou Kai approaches Shin to talk to him and drink with him since it was New Year to celebrate. But Shin starts complaining to her about all his problems. Shin brings up the matter of her being his lieutenant who is also a 3000-Man Commander. He told her that Ryuu Koku said if she keeps working as Shin's lieutenant it would make Hi-Shin Unit an 8000-Man Unit. Which surpassed the body of soldiers which Shin's current rank allows and it does not make sense that Kyou Kai unit would be bound to Hi Shin Unit. But Kyou Kai tells Shin that she will not go Independent and that she will stay with Hi Shin Unit until the very end.
She was seen recruting new members into her unit.
During the attack on Gyou, Kyou Kai was the first one to figure out the purpose behind Ou Sen's locust strategy.
On the third day of Battle at Shukai Plains Kyou Kai was send by Shin to stop the biggest blaze on the battlefield. She set up two anchor points on the sides in order to funnel the enemy straight down the middle and push them back in one swoop with infantry. This allowed her to hold the position and prevent Hi Shin Unit from being wiped out.