Dark Koga

Dark Koga (闇古雅, Yami Koga) is a Dark Side that is made up of all of Koga's negative emotions and given life to by the Hōgyoku.

Appearance
His overall appearance is practically the same as Koga's; they look identical, only with his color scheme the opposite of Koga's. He is a fairly tall and lean-built being with pure white skin and jet black hair. Black pupils, blue irises and black sclera. He also has black nails. While Koga wears a black standard Shinigami Shikakusho, his darker half wears a white Shihakusho uniform with a black cloth belt.

Born from a strange process involving Takashi Sora using the Hōgyoku on Koga to manifest his desires, Dark Koga represents the darkest side of Koga's soul. He has stated himself to present Koga's purest instincts, like an Inner Hollow, as well as all of his hatred, pain, and lonliness. As he resides within Koga's soul, he has become a manifestation of Koga's very spiritual power, meaning Koga's Shinigami powers and even his Seijin powers also draw strength from him.

Personality
Dark Koga is malevolent, sadistic, cunning, and sarcastic, as he is the pure manifestation of all of Koga's darkest and most buried emotions. At first, the Darker Koga wanted to kill Koga, but he soon realized that he shares the same fate as Koga as long as it is only apart of Koga's soul, and not the one in control; so he has no choice but to cooperate with Koga on occasions or he will die along with Koga. After this revelation, he will go to great lengths to preserve Koga's life, as shown when he forces his powers into Koga whenever his life is in danger or whenever Koga's negative emotions surface.

Just as Repressed Seireitou, also known as Sanagi, commented that it did not like the presence of Dark Koga within Koga, Dark Koga has shown indifference towards the Repressed Being, rebuking Koga's friend Seireitou for needing the help of such a creature for his power source.

Dark Koga has a deep hatred for the Kawahiru Family in general and their tremendous reiatsu, likely because of the many times Koga's normal form has been outdone by it (remember, Dark Koga is all of Koga's negative emotions so this trait is caused by Koga's resentment for the Kawahiru's powers).

Seijin Campaign arc
During a Seijin exploratory mission to Hueco Mundo and after a brutal confrontation with Takashi Sora, Koga's team came under the attack of the Arrancar, Xerxes Averian. In the midst of the attack, Koga's friends arrived to assist him and ends up getting dragged into the attack. Koga's reiatsu begins to fluctuate and, after Seireitou's unconscious form is also attacked, he begins to transform into a Seiatsu. Sora later comments that he had the Hōgyoku on his person during his confrontation with Koga's group, and forced it to obey Koga's desires, unknown to Koga himself. Since Koga was desiring to free Seireitou from his Hollow form at the time this was happening, the Hōgyoku began to act on it until the object found something interesting. It somehow realized that Koga's true desires were to protect all of his friends from harm, because his friends were ever so few. The Hōgyoku also realized that Koga could not do this without another source of power, so it lumped all of his negative emotions together to create an inner being called a Dark Side (暗部, anbu) or more specifically Dark Koga.

Powers & Abilities
He has stated that he possesses all of the abilities, powers, and tactics that Koga does but enhances some of them.

Master Swordsmanship Specialist: Since his master, Koga Tensei was trained by the Order's most powerful Grandmaster, Junsui Kirei, Dark Koga also has skill with swordsmanship. Through Koga, Dark Koga inherited a rich tradition of zanjutsu training. Dark Koga's style features elements of many different swordsmanship styles, making him outstandingly talented. Dark Koga is well versed in the classic zanjutsu combat styles, like Otsu (落つ, To smash) which was invented by Genryūsai Shigekuni Yamamoto back when he founded Shinō Academy. Otsu is an aggressive style that focuses on physical strength and sweeping strokes, taking the defensive principles of standard sword-fighting, the style practiced by Gotei 13 personnel, and converting them to offensive moves. With Dark Koga's exceptionally high concentration of spiritual energy and personal skill, he has learned and applied Otsu much more quickly and effectively than even Koga, who is the best trainee in the Seijin Order with Otsu. His skill is further emphasized by his achievement and mastery of Bankai.

Immense Spiritual Energy: Dark Koga has been noted on several occasions to have tremendously vast levels of spiritual energy well beyond that of his Shinigami, possibly due to him being made of the Hōgyoku's energy. He is capable of defeating several Adjuchas-type Hollow shortly after awakening in the Forest of Menos. Even at less than half strength, his spiritual energy is still comparable to a Captain-level fighter; while his full power has not yet been compared to any other fighter thus far, he has been shown to keep up with his master, Koga, fairly easily; even overwhelming him on some occasions. His spiritual power is noted to be something so powerful that reiatsu cannot be compared to it, which surprised Renge Yamato, a Master of the Order. It is often so overwhelming that even when worn-out in battle, he can continue fighting effectively while still capable of unleashing his unique powers, zanpakutō's Shikai abilities, or even unleash and maintain his Bankai. Because Dark Koga's spiritual energy is constantly so high, even at its base level, without him consciously being aware of it, he rarely becomes exhausted in battle, thereby meaning the sheer resilience and amounts of energy Dark Koga has is monstrous. He has learned how to harden his spiritual energy and enhance the strength of his attacks or act as a barrier to reduce the impact of attacks on him, if not negating them completely.

Flash Steps Expert: He is masterful in the art of Flash Steps. He notably makes a massive leap in Flash Steps within mere moments force his opponent wherever he wants them to go in order to allow him to decide his battlefield of choice or to move the fight away from injured or weak comrades.

Enhanced Strength: Even while unarmed, Dark Koga possesses a remarkable amount of strength, being capable of destroying large objects with a single punch. Dark Koga is strong enough to break a large water pipe in two and swing it like a bat. He was even able to battle a Gillian-class Menos with his bare fists, a remarkable feat. His strength is further enhanced with his use of Seijō Reiryoku, allowing him to take on those bigger them himself with relative ease as a single punch was shown able to knock the same giant Gillian-class Menos down with this power. His strength also becomes great enough to block incoming attacks and blasts from Captain-level Shinigami.

Zanpakutō
Ryūjin Koji (龍神虎子, Dragon King, Baby Tiger): Dark Koga has his own version of Ryūjin Koji. When sealed, Ryūjin Koji looks very similar to Toshirō Hitsugaya's Hyōrinmaru; a normal katana with the exception of the guard, which is in the shape of a four-pointed black-colored star. Its hilt is maroon red and sheath dark red. The sheath completely burns up when he draws his sword and somehow reappears once he seals the sword again. The sword is somewhat longer than most Zanpakutō, at about 1.5 meters long, making it taller than Hitsugaya's Hyōrinmaru as well as being taller than Dark Koga himself, preventing him from wearing it at the hip. Instead he carries it on his back by his sash over his right shoulder.

Ryūjin Koji is the strongest of all lava-element Zanpakutō in Soul Society as well as the only known lava-type thus far. As such, Ryūjin Koji doesn't need fire or lava to be present in order for him to use its abilities. Dark Koga's control over Ryūjin Koji's power has been shown great enough to unleash some of its fire and lava powers even in its sealed state and use any of its Bankai attacks (with less control) with Shikai.


 * Akenami (朱波, Scarlet Wave): Dark Koga gathers black flames in Ryūjin Koji's blade and fires it as an arrowhead-shaped burst which has enough power to demolish a small house. The flames also heat up the air rapidly as it is traveling to it's target, which can burn allies and enemies alike who get too close to it's path. He can also keep the flames within the blade and slash at his foe, causing an immense burn and slash mark. The target will be burned regardless if the blade hits or not, due to the immense heat the flames generate.


 * Shikai: Ryūjin Koji is released by the phrase "Burn away the flesh" (熱傷先に其の肉, Nesshō sakini sono niku). When released, Ryūjin Koji's guard is replaced by four "blood-soaked" ribbons and is surrounded by red reiryoku. Soon after, it's blade becomes engulfed in flames. On some occasions, the fire from Ryūjin Koji will engulf Dark Koga in a flame aura that doesn't seem to harm him at all.
 * Shikai Special Ability: Ryūjin Koji allows Dark Koga to control any and all fire, as well as generate fire from the blade itself. His slashes create an immense amount of spiritual power which overflows from the tip of the blade, creating a wave of fire that sometimes can be shaped in a different form, depending on what power Dark Koga is accessing at the time. The flames then fly towards the opponents and instantly incinerates anything it touches. Ryūjin Koji can create multiple flame waves and projectiles to attack an opponent from various angles. Dark Koga can also direct his slashes towards the ground and form a wave of fire which rushes over his opponents, overwhelming and obliterating them, or severely burning them if he doesn't wish to kill them. The very blade of Ryūjin Koji also burns anyone or anything that touches it, including other zanpakutō. The flames of Ryūjin Koji also have another special property; any water the flames come into contact with is immediately evaporated because the heat of Ryūjin Koji's flames far exceed water's boiling point. However, it is not a fire type Zanpakutō. Instead, it is a lava-type. It's blade can generate lava in the same manner that it generates fire and can turn any source of fire into lava or magma, and as such it is the strongest Zanpakutō of it's kind. When the lava makes contact with a foe or any object, it not only fatally burns the target but also hardens quickly, forever encasing the target in hardened lava.
 * Honōtama (炎弾, Blaze Bullet): A much large, faster version of Akenami, this attack functions much in the same way. A notable difference in it's use from Akenami is that, upon contact with the ground, it's flames spread to engulf whatever it has struck, creating more flames for later attacks.


 * Yōganryū (溶岩流, Lava Flow): Dark Koga launches a rushing surge of black lava at his enemy. The torrent of high pressure lava and fire is large enough to cover several town blocks and kill anything that is unlucky enough to get caught in it.


 * Yōgansentō (溶岩尖塔, Lava Spine): This ability creates a pillar of black fire and lava that trap an opponent and makes it impossible for them to escape for some time. Dark Koga can create up to ten of these pillars to hold his foes.


 * Enkō no Mai (炎光の舞, Flame Dance): Dark Koga will call out the name of the technique, and then begins to build up flames, firing toward the target in a massive, powerful tsunami-like wave of fire from Ryūjin Koji's blade, in turn incinerating the target.


 * Bankai: Torahasami Ryūgenko (虎螯竜拳固, Tiger claws, Dragon fist): In Bankai, the blade of Torahasami Ryūgenko doesn't change at all from it's Shikai state, however, aqua-colored crystals have now grown out from the bottom of the hilt and encased his sword hand. Upon activating Bankai, fire engulfs the area around or below Dark Koga for several kilometers and brings forth an enormous, gray dragon standing at nearly one hundred meters tall. The dragon has the head of a typical Chinese dragon as well as the Chinese dragon's serpentine form. It has four large wings and two arms along it's body. Another noticeable change in Bankai is that Dark Koga's eyes change from blue to yellow for the duration of the time he is in Bankai. Torahasami Ryūgenko does not follow the general naming scheme of zanpakutō Bankai. Instead of incorporating a new name to the already existing name, it creates a new name entirely.
 * Bankai Special Abilities: Torahasami Ryūgenko's Bankai has several additional techniques aside from the abilities of the dragon and the Shikai.


 * Dragon Control: The giant dragon copies the movements of Dark Koga (in a similar manner to Komamura's Bankai) to devastating effect, allowing it to deal out colossal amounts of damage. Its strength is far proportionally greater than that of Koga due to its size. It is strong enough to take an Arrancar's point-blank Cero without being damaged, and could easily smother him with its bare hands. It can also blast flames and lava from it's mouth.


 * Lava Clones: Dark Koga is able to create and mold a large amount of fire and lava into his exact likeness. It is very life-like as it can appear to bleed. He seems to be able to use this power more than once.


 * Hariganshō Tensū (玻璃岩漿点数, Crystal-Magma Points): The crystals encasing Dark Koga's hand break off and float in place around his head. They then spontaneously ignite and are hurled at incredible speeds at a target. After piercing the target's flesh, the burning crystal will then sear and cut internal organs and veins which becomes fatal to the target.


 * Shield of Magma: This ability was first demonstrated in his Bankai, however, he has shown the skill to use it in Shikai also. He will create a burst of magma from the tip of his zanpakutō which spreads out to form an immense shield, shaped like a flower, which then hardens quickly, protecting him from all but the most powerful techniques.


 * Shininohonō (瞋恚の炎, Flames of Rage): This technique is an offense upgrade of the Shikai's Yōgansentō power. It creates a pillar of magma, which seems to erupt from the ground, followed by ten more pillars exactly like it. At Dark Koga's command, the pillars will all launch towards a target, catching it within the middle of them, and incinerate that target.


 * Meramera (めらめら, Bursting into Flames): Considered by Dark Koga to be Torahasami Ryūgenko's most useful ability, it allows him, with a mere gesture of his blade, to convert any oncoming energy attack into magma for his attacks. He has shown the skill to use this power in Shikai as well.


 * Shittonohonō (嫉妬の炎, Flames of Jealousy): Considered to be Torahasami Ryūgenko's most powerful ability, Koga will create tremendous amounts of magma which quickly encircles a target and traps them within a giant sphere of this magma. It incinerates anything inside of it and then hardens, forming a large mass of hardened magma the size of a large mountain, keeping a surviving target, should there be one, forever trapped within.
 * Otaki Yōgan (小滝溶岩, Cascading Lava): In the rare occurrence that someone should survive Shittonohonō, Koga has a fail safe. If the victim escapes, he will immediately convert the large mass of hardened magma back into hot, flowing lava and cause it to be launched down on the foe, in a similar manner to Yōganryū from the Shikai. The amount of this lava is so great that it can effectively fill and destroy a large town with ease. Dark Koga is positive that the heat alone is fatal, but anyone caught in the lava itself is doomed to die a painful death.

Possession of Koga
Whenever Dark Koga takes control of Koga's body, it spurs an odd transformation.

Evolving Transformations: Unlike Vizard, who summon a Hollow Mask to utilize thier powers, there is no such thing for a Seiatsu. While Koga is unable to control his Dark Side at the moment, Sora has admitted that there is a possibility to control the form and doing so would make Koga tremendously more powerful. The first signs of a transformation is Koga's eyes turning into that of a Hollow's, black pupils, yellow irises and black sclera, as well as his hair turning dark grey and lengthening slightly. As the transformation progresses, a white liquid erupts from the buckle on his zanpakutō strap and covers his body, hardening in the process. In this new form, he appears as a phantom-like figure. His face is covered with a white canvas and his outfit is now a white cloak that is split in four sections near his waist, similar to coattails. There is a cross in the middle of the cloak, showing where the clip to his Zanpakutō strap is, which is were the substance originated. Also, when he is attacked, his body appears to crack and fold under damage, only bleeding when an attack is powerful enough. This form is eerily similar to Sōsuke Aizen's transformation during the Winter War, only it seems to take place backwards, with the hollow-eyed Human stage coming before the so called "chrysalis form". If the transformation progresses even further, not much changes in his appearance. He begins gaining coattails until he has a total of nine, signifying that his transformation is complete.


 * Enhanced Speed: Dark Koga manages to move at exceedingly incredible speeds, quick enough to appear behind the likes of his Master, Junsui Kirei's back and effectively counter him before the former could even turn to face him.


 * Enhanced Stamina: He can effectively continue fighting for several hours in advance, showing no sign of tiring or injury to himself.


 * Enhanced Strength: His strength has now increased to the point, where he can pick up and even throw the gigantic form of Zacarias Donato's released form with little to no effort.


 * Enhanced Durability: Dark Koga's durability has greatly increased, able to withstand several large explosions in his battle with Xerxes Averian at close range with no visible damage. His skin and hands are also strong enough to catch and hold onto Xerxes's strongest attack. He has also shown himself capable of withstanding incredibly brutal beating from foes without showing signs of pain or even care.


 * Enhanced Spiritual Power: Since the Hōgyoku transfered it's unique energy into Dark Koga as the transformation's main power source, Koga now has dual-type spiritual energy which is half Shinigami, half Hōgyoku. Like the Hōgyoku energy, Koga's spiritual power becomes overbearing, unlike anything else in Soul Society, and completely unrelated to reiatsu. His energy increases as his transformation progresses. By the completion of his transformation, his spiritual energy has reached a whole new level. Renge comments that it is the largest amount of spiritual energy he has ever seen in one body.


 * Enhanced Telekinesis: His Seiatsu powers even effect his Shiro Nagare manipulation of his Seijin powers. Of all his new powers, this one is the only one that will remain outside of his transformations. His telekinesis is now deeply linked to his emotions. During flashbacks that prove emotionally painful for him, the outside world is noticeably affected by earth tremors and the cracking and smashing of nearby objects, all caused by telekinesis.


 * Sara (皿, Disc): This technique, named by Dark Koga himself, creates an energy disk about the size of Koga's palm. The disk can then be fired, slicing through anything it comes into contact with. Dark Koga has also shown the ability to cause the technique to expand in mid flight to allow it to cover a much larger radius.


 * Regeneration Powers: The cloaked form of the transformation has been demonstrated to actively protect Koga by healing his injuries almost instantly.

Trivia

 * His personality is heavily based on that of the Nine-Tailed Fox's from Naruto.