Kōga Kuchiki (朽木 響河, Kuchiki Kōga) is a former 3rd Seat of the 6th Division who later revolted against the Seireitei. He was also a member of the Kuchiki noble family, having married into it. Years after he died his body was retrieved by Inai Satonaka.
Kōga has piercing green eyes and shoulder length black hair and a long ponytail of red hair, with a short tufts of red hair on the left side of his head, and bangs that hung on the right side of his face to frame it. When he was a member of the Gotei 13 he wore a standard Shinigami Shihakushō, along with a long red scarf and a light lavender obi sash, with a beaded-necklace with a pendent. He also wore an intricate white headpiece called kenseikan on the left side of his head to symbolize his nobility that held his ponytail in place with red tufts of hair sticking out (which he later cut off to relinquish his status as a Kuchiki).
While originally his appearance was youthful and fit, after several hundred years sealed away, his physical form has been reduced to a withered-old version of his former self.
Kōga is a man with a true sense of duty and a commitment to making his family proud. He always tried to remain humble and serious to situations at hand. On the inside however, Kōga was a man who deeply desired to be acknowledged for his abilities and hard work. After being betrayed and realizing that his life as he knew it was gone forever, he had a mental-breakdown, causing him to become consumed by his anger and desire to stand in greatness, leading him to become immensely arrogant in his power to the point of viewing all others as worthless, even his own Zanpakutō, Muramasa.
Several hundred years before the current time, Kōga was welcomed into the Kuchiki family as the son-in-law of the Ginrei Kuchiki. He soon gained much respect throughout Soul Society. He in his capacity as the 3rd Seat of the 6th Division participated in a battle between the loyalist and rebel factions of Soul Society winning a decisive victory for the loyalist side single-handedly. For his role Kōga was given much praise and accolades for Captain-Commander himself. Ginrei grew increasingly concerned about Kōga's overconfidence in his powers and made a point to address that he needed to to control himself. Kōga took this in stride but never could understand why Ginrei never acknowledged any of his achievements. He would increasingly speak to his Zanpakutō, Muramasa about this only increasing his overconfidence. As he engaged in battle after battle winning each one with ease, for his efforts he is given a special position by the Captain-Commander, making him the captain of a special force directly under his authority that is totally dedicated to wiping out the remaining rebels. When it became clear that he may very well be the key to winning the war, the enemies, which included three elites, came up with a plan to frame him as a traitor. They achieved this by having their own men attack Kōga knowing he would easily dispatch them and then charging him with the murder and having him arrested. Ginrei arrived to see what happened but upon one of the fallen soldiers admission that Kōga sacrificed them for his own battle lust, he had no choice but allow Kōga's arrest until he can determine a way to clear him. Ginrei visited him in jail and detailed that his punishment had been handed down. He is for the next few hundred years to be suspended from his seat in the 6th Division and it was determined that his Zanpakutō was a threat to the peace, therefore its powers would be nullified. Ginrei noted to him that he didn't believe any of it but that the top brass had a problem with his Zanpakutō and its ability. He further explained that they weren't afraid of him but Muramasa getting out of control. Ginrei then left Kōga there to learn patience as he went to rectify the situation. Kōga was later freed by Muramasa who inspired him to take control of his life again
That night Kōga killed the elites who framed him. Upon hearing of this Ginrei went in search of Kōga and found him in the outskirts of Soul Society. Ginrei confronted him about his actions, and Kōga explained that he killed the elites for their betrayal, hoping that deep down, they would regret their choice to frame him, but he had found them laughing. He noted that even after killing them he was still filled with so much anger for what they had done to him and the humiliation he had endured. Ginrei remarked that any chance at proving his innocence is gone and that his rashness now put him in a worse position and he will probably be executed. Kōga, upon hearing this, suffered a breakdown and accused Ginrei of being like all the others and being jealous of him. Kōga decided to stage a personal revolt against Soul Society and all his enemies. As he killed more people his instability grew. When Muramasa noticed that Kōga's heart has become turbulent, he tried to tell Kōga to forget the past and focus on the future, but Kōga became obsessed with the idea that everyone hated him and that he couldn't understand why. While fighting against a group a Shinigami, he attempted to release Muramasa and found there was no response. He tried again and Muramasa appeared. While he sat alone in a cave Muramasa appeared as asked him why he would kill innocent bystanders, to which Kōga remarked that he was teaching Soul Society a lesson for exiling him from their world. Soon he was even abusing Muramasa when he was anything less than absolutely obedient. This disharmony between them gradually caused Kōga to lose his ability to communicate with and even access Muramasa's power. Eventually Genryūsai Shigekuni Yamamoto and Ginrei Kuchiki confronted Kōga, and after an exchange of words, they realized that they couldn't get through to him. They engaged in a minor battle and Kōga went to release Muramasa with no results. The two captains take advantage and move to seal Kōga away when they realized he lost total access to Muramasa's power.
Kōga's revolt was never recorded in the Soul Society's history
Kōga was sealed away, but his ZanpakutōMuramasa eventually resurfaces and begins to initiate a Zanpakutō Rebellion. When Ichigo Kurosaki encounters Muramasa, he states that he already killed his master. However, after Muramasa gains control over Ryūjin Jakka, Genryūsai Shigekuni Yamamoto reveals that Muramasa is planning to break Kōga's seal. He also states that Muramasa is heading to [[w:c:bleach:|]], where Kōga was sealed.
Muramasa eventually arrives at the location where Kōga was sealed, but comes into conflict with Orihime Inoue, Uryū Ishida, Yasutora Sado, and Rukia Kuchiki. He ultimately succeeds in breaking Kōga's seal.As Ichigo arrives to stop him, Kōga begins to awaken. Though Muramasa is ecstatic that his master is finally free, Kōga immediately stabs him in anger, leaving a shocked Muramasa to ask him why.Believing that Muramasa abandoned him before being sealed, Kōga decides to reinforce his status as master by making Muramasa pay with his life. However, Byakuya appears, stopping Kōga's strike and scolding him.
Kōga notices that Byakuya is wearing the ginpaku kazahana no uzuginu scarf and the kenseikan and asks him if he is a member of the Kuchiki family to which Byakuya tells him his name and notes that he is the 28th Head of the Kuchiki family. Kōga then questions if Ginrei finally died but Byakuya scolds him for even saying the name. As he had no right to speak it after he soiled the Kuchiki families name. Byakuya reveals that he pretended to betray Soul Society so he could put the shame of Kōga to rest. After learning that Byakuya is the current head of the Kuchiki clan, Kōga becomes determined to destroy his association with the Kuchiki clan by killing its leader. Muramasa, despite being attacked by his master, insisted that Kōga use his power. Kōga arrogantly instead destroys the remainder of his sword, casting Muramasa away completely. Kōga retrieves one of the blades that sealed him and engages Byakuya, fighting him on even grounds. They leave melee combat in order to face off against each other using Kidō, to which Kōga uses the Kongōbaku, Gaki Rekkō and Hyōga Seiran in successive order to which Byakuya counters with Sōkatsui, Byakurai and Danku respectively. After freezing the surrounding lake with the Hyōga Seiran spell, Kōga also succeeds in encasing Byakuya in ice as well. Byakuya breaks free using Senbonzakura and then Kōga attempts to attack but Byakuya moves away allowing Kōga to use his spirit threads to hold Byakuya in place. Byakuya releases Senbonzakura and frees himself as well as attacking Kōga who tries to deflect Senbonzakura's blades but only succeeds in breaking his own weapon.
Byakuya uses the opening to finish him off but after cutting Kōga he realizes that it was just an illusion leaving him open to be attack. Kōga uses his illusions to show Byakuya he is no match for him and explains his ability and notes that had Byakuya closed off his "heart" like Ginrei and Yamamoto did when he was challenged by them he would have never been able to use his technique. He taunts Byakuya for letting down his guard because he discarded Muramasa. Byakuya tells him that he is wrong and that he didn't close off his "heart' because his intent was to kill him, had he closed off his "heart" he could just seal him away again but not have killed him. Byakuya then attempts to release Senbonzakura but Kōga quickly counters and throws another blade weapon at him while using his illusion ability to confuse him allowing the weapon to catch Byakuya's sword hand knocking Senbonzakura out his hand and across the frozen lake. Another blade weapon is thrown but Byakuya dodges, Kōga uses the Hyōga Seiran spell again to which Byakuya tries to block with Danku. He realizes it was an illusion as he is hit from the side encasing him in ice and putting him at the mercy of Kōga. He gloats over how great his power is and attempts to finish off the incapacitated Byakuya only to have his weapon stopped by Senbonzakura. Kōga is surprised as he notices the Zanpakutō has released itself from some distance away to protect its master.
Byakuya breaks free and readies himself against Kōga who has determined to affect his Zanpakutō's perceptions as well. Before he can attempt it Byakuya releases his bankai and uses his Senkei technique. He notes to Kōga that this is Senbonzakura's true form and that it is all about offense and no matter if he can affect his perceptions as no matter where he is in there his blades will aways find him. The two face off against each other in stalemate until Kōga uses his spiritual threads to bind Byakuya but many of Senbonzakura's blades rain down cutting the threads much to Kōga's surprise. Byakuya attacks him but he moves out of the way and asks, how Byakuya can be so powerful? Byakuya plainly states because it is both him and Senbonzakura fighting him. He further explains that Shinigami and Zanpakutō are two in one and that they only reach their full potential when their two souls resonate with one another. Someone like Kōga who casted everything aside for his own vanity could never defeat them. Kōga refuses to listen and states that his greatness was never acknowledged and that he was betrayed so he turned on them all and would create a world of his own choosing and be king. Byakuya calls him foolish as his real tragedy is that he failed to see where true power lies. He remarks to Kōga that the power he needed was to communicate with others as well as his Zanpakutō. Kōga refuses to believe that as he considers his powers unique and thus makes him superior. Byakuya then refuses to try to appeal to him any longer and curses him for his immaturity that prevents him from seeing his own overconfidence. He then activates his Shūkei: Hakuteiken technique to which Kōga states it impressive as their isn't many heads of the Kuchiki family that were as powerful as him. Byakuya explains that he is using this technique on him as a final act of respect to him as a former member of the Kuchiki family.
The two clash and in the aftermath, Kōga is defeated. Refusing to admit defeat, he calls for Muramasa to aid him. But like centuries ago, he is shocked to see that Muramasa does not respond, forgetting that he had already severed his bond with him. Failing to see the truth, Kōga falls into the depths of the lake and dies.
Master Swordsmanship Specialist: Kōga was an immensely powerful combatant, even with only his sealed Zanpakutō. Back when he was only a 3rd seat officer, he was able to easily fight at captain-level and take down a large group of enemies attacking him at once.His skills are very versatile, able to use various bladed weapons with high proficiency. His skill allowed him quick and precise strikes that rivaled that of Byakuya Kuchiki.
Shunpo Master: Kōga has demonstrated highly proficient skill in Flash Step, able to keep on equal footing with Byakuya Kuchiki, one of the most skilled masters. In battle, Kōga has shown great enough reflexes to dodge point-blank sword attacks unscathed.
Kidō Expert: Kōga's skill in Kidō is immense, able to use various forms of spells with great power and skill successively; all at the same time without incantation.
Enhanced Strength: Even in his physically withered state, Kōga is deceptively strong. With a single downward chop, he was able to snap his sword's blade in two.
Immense Spiritual Power: While not a noble by blood nor of considerable age, Kōga possessed great spiritual power even when only a 3rd seat officer. Ginrei, the 6th Division captain at the time, states Kōga's power vastly surpasses his own. He displays a massive reiatsu, even after being sealed away for several centuries. His reiatsu is purple in color. His skill and control at using his spiritual energy allows him to perform a variety of abilities.
Illusions: Muramasa can control other Zanpakutō but its ability is just apart of Kōga's own special ability. He can send his reiatsu into his enemies and and throw off all of their senses. He then has complete control over what they perceive. Thus making it so his opponent cannot even see him clearly though he is right in front of him. Kōga states it is so much more then simple illusions. This power can be negated by one closing their "hearts" off before challenging him.
Spiritual Threads: Kōga is able to form invisible spiritual threads to bind his opponent in place. While powerful, these threads can only be manifested through a reflective surfaces such as a building's windows or clear water, where they can be seen. In turn sufficient cutting can easily break the the threads.
Muramasa (村正, Village-Just): Kōga's Zanpakutō takes the form of a katana with a dull red sheath, purple hilt-wrapping and a guard in a shape similar to the Kidō Corps' emblem, consisting of a circle with a pentagon-like shape in the center and three points protruding from the edges evenly spaced apart. Muramasa is an illusion-type Zanpakutō.
Shikai: The release command is "Whisper" (囁け, sasayake). Muramasa shines with bright purple light to engulf a considerable radius, affecting any and all targets within it.
Shikai Special Ability: Upon release Muramasa glows purple and releases a 360 degree wave of purple energy into the surrounding area causing all Zanpakutō in that area to turn on their wielder. The Zanpakutō will move on their own against their wielders will and attack their allies or even turn against their own wielder. This power is shown to effect around 10 individuals at once. It can cause a Zanpakutō's spirit to abandon its master and attack them. The only way to combat against Muramasa's power is by understanding how the Zanpakutō works and sealing one's "heart" against it. Though in order to block the attack in that state one must have incredible reiatsu and concentration. In addition, one must be able to still fight in that state.
Yūkōjōchū Muramasa (有鉤条虫村正, Hooked Tapeworm Village-Just): upon a large explosion of spiritual energy, Muramasa manifests its true form into the real world. Muramasa himself has the ability to manifest in his true form and even can manifest himself at a distance from his master, able to hear his call from wherever he is. Muramasa can also manifest his sealed sword form and engage his powers independently of Kōga's command.
Zanpakutō Manifestation: Muramasa generates a burst of energy that affects the Zanpakutō of all in the vicinity. When this takes place, the Zanpakutō of other wielders glow with a purple light. Their Zanpakutō spirits then manifest, typically as tangible shadowy figures from weaker Shinigami and with greater individuality and power from stronger Shinigami. Muramasa can break into the inner world of targets, similar to how a tape-worm leeches off its target, and forces them to bend to the user's will. This is done by removing the energy stability between Shinigami and Zanpakutō, leaving the spirit confused and allowing Muramasa to forcibly release the Zanpakutō spirit's negative emotions.