Kaguro

Kaguro is a villain from the anime Kekkaishi, a member of the Kokuboro, a group of strong Ayakashi, (ghosts or demons).
 * A S-Class Ayakashi, Kaguro is one of the few members of the Kokuboro to act on his whim while possessing superhuman speed and able to generate blades from his body. Kaguro was once a human swordsman named Genichiro Kuroda (黒田 源一郎 Kuroda Gen'ichirō), a student of a dojo who was friends with his rival Sakai. But unable to beat Sakai, Kuroda's frustration and his friend's advice, misunderstanding the meaning, led him to go on a killing spree. In the process, Kuroda lost his humanity and killed Sakai prior to assuming his current form. Donning a human skin and leading a group of Akayashi in an attempt to take over Karasumori, Kaguro develops an interest in Yoshimori, who is unknowingly able to use Zekkai, a technique that Kaguro saw first hand when he was still human. After killing Gen, whom he attempted to have walk in his footsteps, Kaguro battles Yoshimori in the collapsing Kokuboro castle before being killed in battle by the kekkaishi.
 * A S-Class Ayakashi, Kaguro is one of the few members of the Kokuboro to act on his whim while possessing superhuman speed and able to generate blades from his body. Kaguro was once a human swordsman named Genichiro Kuroda (黒田 源一郎 Kuroda Gen'ichirō), a student of a dojo who was friends with his rival Sakai. But unable to beat Sakai, Kuroda's frustration and his friend's advice, misunderstanding the meaning, led him to go on a killing spree. In the process, Kuroda lost his humanity and killed Sakai prior to assuming his current form. Donning a human skin and leading a group of Akayashi in an attempt to take over Karasumori, Kaguro develops an interest in Yoshimori, who is unknowingly able to use Zekkai, a technique that Kaguro saw first hand when he was still human. After killing Gen, whom he attempted to have walk in his footsteps, Kaguro battles Yoshimori in the collapsing Kokuboro castle before being killed in battle by the kekkaishi.

Kaguro was one of the strongest Ayakashi in the Kokuboro (and therefore one of the few able to resist Byaku's control worms). Though he does not participate in the leaders' meetings, Kaguro has a great deal of influence among them, and is often sent to Karusumori in human skin to observe attacks on the Kekkaishi. Kaguro is eventually defeated by Yoshimori

Appearance
Kaguro is always wearing a human skin disguise while in Karasumori: a tall, pale man with red eyes and dark hair. Though it is an older model and Aihi has designed more up-to-date ones, Kaguro prefers it, considering that the limits it places on his powers provides a fun challenge. When not in his human skin disguise, Kaguro appears as a mummy with large eyes with red irises and yellow sclera, and always wears a black robe with red, frayed trim. The exposed portions of his skin are badly burned, as his transformation into an Ayakashi greatly resembled him being struck by lightning.

Personality
Kaguro is calculating, sadistic, and cunning. He hangs back and observes in many battles, looking for a single opponent who captures his interest. Once found, he pursues and provokes them with mind games until the two meet for their final battle. He also enjoys manipulating the other demons in Kokuboro, and does not consider cutting them down a betrayal, because in his own words, he has no allies. Kaguro also has some sense of personal honor: he despises taking hostages and prefers to challenge enemies directly in combat.

History
Kaguro was once a skilled human swordsman named Genichiro Kuroda (黒田源一郎, Kuroda Gen'ichirō). He taught himself to use a sword and joined a dojo, becoming one of the top students. He competed Genichiro Kuroda with his friend and rival Sakai to be the master's assistant, but was never able to defeat Sakai. Kuroda was frustrated and wanted to become stronger, but didn't know how to go about it. Sakai told him that he was already strong because he never hesitated, and that if he simply wanted it badly enough, he could become stronger than anyone. Kuroda misunderstood Sakai's meaning and began challenging and killing the best swordsmen he could find. Kuroda was thrown out of the dojo, and some time after that encountered and fought a Kekkaishi. The Kekkaishi sensed the darkness within Kuroda, and proclaimed that the only reason that Kuroda could cut through Kekkai was because he was no longer human, but a demon, and as such, it was a Kekkaishi's job to destroy him. The Kekkaishi then used a Zekkai, but the very sight of it scared Kuroda away.

Kuroda ran to a riverbank, where he found three Ayakashi on the other side. They invited him to cross over and join them, where he would become stronger, but Sakai suddenly appeared. Feeling responsible for Kuroda's rampage, he challenged Kuroda in an attempt to save his soul. Sakai nearly defeated Kuroda, but hesitated when he saw Kuroda's fear. Kuroda took advantage and killed Sakai, becoming an Ayakashi and gaining entrance to their world. At some point after this, he joined the Ayakashi group Kokuboro.

When Teasing Hisui
Aihi allows Hisui to try on an old model of her human skin disguise. Kaguro tells him it's pointless, since Hisui was weak to begin with, and the disguise would only limit him further. He also implies that it wouldn't be a problem for himself, since he is strong enough. Furious and determined to prove himself, Hisui rushes to Karasumori. Aihi tries to stop him, but Kaguro stops her. Aihi accuses him of having done that on purpose, and Kaguro agrees, saying things were getting boring, and that this will give them something of interest while Aihi finishes the improved disguises.

The Squad of Kaguro
Kaguro volunteered to lead the group of Sanan, Haizen, Sekia, and Haroku to Karasumori. Aihi provides each Ayakashi with a human skin disguise so they can move about safely during daylight and avoid detection. Kaguro chooses an older model, amused by the challenge of the limits it places on his power. Kaguro's group enters Karasumori Academy, drawing some odd looks but meeting no major obstacles as they head to the broadcast room (with the excuse that they're from a hidden camera television show). They announce themselves as Kokuboro, finally drawing the attention of Yoshimori, Tokine, and Gen Shishio, then ask them to meet at the usual place (Karasumori) to negotiate. Kaguro's group leaves the school before any of the three can stop them.

At Karasumori that night, Kaguro makes an attempt at being civil: his group gives the Kekkaishi and Gen a chance to surrender and allow Kokuboro to take Karasumori without a fight. Naturally, the Kekkaishi and Gen refuse, and Gen rushes at Kaguro, sensing that he is the strongest. With startling speed and ease, Kaguro beats Gen, then destroys Madarao and Hakubi as well. The other Ayakashi carry Gen away, leading Yoshimori and Tokine into a trap: an arena lined with stones that cancel out Kekkaishi powers. Kaguro sits back {C Kaguro destroys Sanan and Sekia to watch the battle. When Gen recovers enough to rejoin the fight, Kaguro draws him away from the others, defeats him easily again, and continues observing the fight. He is disappointed by what he sees: even without Gen, the Kekkaishi manage to escape the trap and destroy Haizen and Haroku. Kaguro finally loses his patience when Sanan and Sekia resort to holding Tokine hostage, and kills the two without warning, releasing Tokine. Kaguro is fascinated by the malevolent aura that Tokine's being held hostage produced in Yoshimori, and would like to fight him again once it has been developed. He recovers the discarded human skins and leaves.

Powers & Abilities
Kaguro was among the strongest Ayakashi in Kokuboro: Byaku's worms could not control him, he had influence even among the organization's leaders, and all other demons were wary of him. Superior Swordsman: As a human, Kaguro was a highly skilled and motivated swordsman, and this was still true as an Ayakashi. Superior Speed: Kaguro moved so quickly that it was extremely difficult to target him. This was especially true for a Kekkaishi, who would need time both to target and create a Kekkai: moving closer would put them within range of Kaguro's swords, and at a distance Kaguro had even more time to read their movements. {C {C Master Strategist: Kaguro enjoyed toying with his opponents in battle, frequently taunting and enraging them. By doing this with Yoshimori, he discovered that the strength of a Kekkaishi's Kekkai depended more on their skill and feelings than their power.
 * Sword Generation: As an Ayakashi, Kaguro had the ability to grow sword-length blades from virtually anywhere on his body (though he most often preferred his palms), and could strengthen them by channeling his desire to destroy into the blades (though they could destroy most Kekkai even at the lowest setting).
 * Anti-Regenerative Damage: According to Kyochi Hiba, wounds caused by Kaguro's swords could not heal normally: cell activity in the impacted areas slowed down, so the wounds remained open far longer than they would normally. This would increase the chances of Kaguro's victims dying from blood loss. This ability even slowed down both Ayakashi Majiri and Ayakashi regeneration.

Trivia

 * Kaguro's name (火黒) means black fire.
 * Kaguro's appearance and personality are in great homage to the design of Shishio of the Rurouni Kenshin series.
 * Kaguro may also represent lightning speed, because he was turned into an Ayakashi with a lightning bolt in the anime.