|Alias||Black Winged King
Since the attack on Jaula Blana orchestrated by Gilbert Ross that took the lives of several of his classmates including Dr. Health Flick, Koku has spent the last seven years in search of his love, Yuna in hopes of reuniting with her.
Koku has heterochromia iridum, and has long black hair. Typically wearing his blue shirts and white capris, Koku looks very quiet and observant.
He is also the black winged king. In that case, his left eye turns into a blue green and his skin black. Two black wings sprout from his back. Most notably, his left arm turns into blue steel on command and is used as a weapon. His left leg, taken from Izanami, is able to turn into steel on command, and is also used as a weapon.
Quiet and nice, Koku brings red bean buns to his employers family. He is skilled at fixing violins but doesn't play them himself.
His secret self as Killer B has a different personality. This personality is more aggressive, solely focused on his goals. He doesn't show mercy as he kills all his enemies and even seemingly common criminals.
First introduced as trying to give some red bean buns to a comically late Lily, Koku is portrayed as quiet and kind. He works as a craftsman at Lily's family violin shop, having a knack at restoring violins to their former glory. In reality, Koku is actually the mysterious Killer B, chased down by the elusive and mysterious Market Makers. Koku is killing other criminals while leaving behind a mark that looks like a "B"and some slashes next to it. He seems to be on the search for someone but can't fully remember who or what happened to him. As the police and RIS are on the hunt for the Killer B, Koku continues to clash with the Market Makers as they use seemingly common criminals to lure Koku out. At the heel of Koku and Market Makers is detective Keith and Lily. Keith seems to know more than he lets on, and aware of the presence of a third party as the police and RIS try to track down Killer B. Lily also picks up on the missing connection between the killings of Killer B and a third party but is told by Keith to stay out of it for her own good. Nonetheless, she continues to investigate.
In the first episode, degenerate criminal brothers are killed off screen by a vigilante in the middle of one of their kills. One of the brothers, Julian, who was monitoring his brothers survives this attack and swears revenge. The killer leaves behind a mark, "B" with some slashes, connecting this kill to other kills also marked with a B. The RIS, including Lily and Boris, are investigating the crime when Lily spots a regularly dressed man trying to entering the crime scene. As she approaches to deny access, he reveals he works for the RIS and is Keith. Unaware who that is, Lily continually tries to tell him to leave until Boris greets him warmly. Keith is actually a detective that left a long time ago, but has returned in light of these new murders.
Julian, bent on getting revenge for his two brothers is approached by a mysterious person with clown tattoos. This person seems to have quite the bit of pull and knows exactly what to do to draw Killer B out. Their plan is to take a tank and wreak havoc all over town before then disappearing in a tunnel. Inside the tunnel, the mysterious clown man has his teammates take care of the tank while he takes Julian to the train. On the train, once Killer B shows up, Julian is disposed of by the mysterious man, saying that his use has come to an end. The mysterious man, Quinn, attacks Killer B, but is easily overwhelmed and killed. His teammates realize his demise is inevitable and move to leave him and the tank to make their own getaway as the RIS and Keith have realized that the criminals were using the old underground tunnels to make their getaway. In the aftermath, the RIS find the train wrecked into the shape of a "B," and wonders how Killer B could control such a thing.
In the second episode, Koku is seen working in Lily's father's violin shop along with her brother. Both men are in awe of his skills and Koku tells them he enjoys being a craftsman because even if he dies a part of him will still live on in the violins he fixes.
The assemblyman Ed Kyle is dead, along with the marking of B, although Keith suspects it not to be actually Killer B. Instead, it is another terrorist intent on attacking the mayor. These terrorists are also being used by the same mysterious organization that aided Julian, with markings similar to a clown. They planned to lock down a gala with the threat of a poisonous gas that will release unless their demands are met. However, while the RIS is dealing with these terrorists, Koku meets with one of the clown tattooed members, Izanami, on the roof of the building. They talk and Izanami states that he was surprised that Koku would be lured in with such easy bait and that "that person must be special," but says that Koku probably doesn't even remember who that is. Taunting Koku with the information that he wants so desperately, Izanami says if he comes with him, he will tell Koku what he wants to know. Koku doesn't take the bait and prepares to attack.
The third episode starts out with Koku and Izanami about to start fighting, and when they do, lights and sounds from their battle attract Keith's attention. As Izanami leads Koku away by skateboard, Koku follows with his wings. Keith hijacks Boris's car and starts to chase after them. When questioned by who they are chasing, Keith can't give an answer to Boris but just feels that he is on the brink of something. The other terrorist members are eventually killed by Izanami's organization and the other RIS members are dealing with the release of the gas, which is revealed to only be knockout gas and not the poisonous one.
Izanami and Koku reach a lake and talk a bit more about the missing person Koku wants to find but can't remember. Izanami taunts Koku saying Koku can't even remember much about himself and he can hear his desperate shouts for attention. As Koku turns into his black winged form, with his blade, Izanami states that he's been thinking about who locked away Koku's memory and has come to the conclusion it was Koku himself because he wanted to forget everything that happened on that day, but that he doesn't want Koku to forget about him. Izanami then reveals his left leg has the same ability as Koku's left arm to turn into a sword. After a fight, Koku is able to defeat Izanami. Izanami requests Koku to take his leg as it will of use to him in the future and to "Touch Canopus." By the time Keith and Boris arrive to the lake, Koku and Izanami's body is no longer there to be found.
Koku is seen in episode 4 to be walking on the streets headed to the Royal Library. On the way, he is spotted by Lily, driving by. As he gets a ride her, he asks Lily if she knows what Canopus is and is surprised when she knew it was a star. Koku arrives at the library and right as he walks in and Keith, also at the library, walks out, Izanami's words "Touch Canopus," rings in his head. However, as he turns around, he doesn't notice anything out of the ordinary and continues into the library.
He is then seen again, reminiscing his fight with Izanami and his words to "Touch Canopus," and remembers the image of a little girl with pink hair. As Koku looks up to the stars, specifically, Canopus, he sets his mind to eventually reach it.
In episode 5, there has once again been an attack credited to Killer B. However, the victim was not a common criminal, but rather a member of the RIS, Bran, after he discovered that all the cameras on phones or computers was actually recording and being monitored. Meanwhile, Koku is at the violin shop when a voice in his head telling him to "Touch Canopus," and when he looks outside the window he sees Keith and Lily. He decides to follow them and spends the day trailing the two of them, specifically Keith. He listens in on his conversations all day, including his conversation with doctor friend, Gilbert, including his curiosity of Ahab's last thoughts before going up against Moby Dick.
Bran survives the attack, and gives Keith a watch. Keith is able to crack the code within the watch and determines it was not actually Killer B that attacked him, but another member of the RIS, Jean Henri Richard. Jean Henri Richard refuses to tell Keith anything but admits that he is in fact part of the mysterious group, and has been in it for the past 8 years, surprised that Keith continued acting like his friend even when he suspected it. Instead of revealing anything to Keith, Jean Henri Richard opts to slit his own throat, and while Keith tries to save him, he is knocked out by Koku and taken to a roof. When Keith awakens, he is instantly aware that he is in the presence of Killer B.
On the roof and in episode 6, Koku demands Keith to tell him about himself and where Yuna is. Keith refuses to tell him anything, but tells him to meet him tomorrow at Heian-ji, where he will tell him everything because he needs to show him something. Keith knows that the B sign is actually a cry for attention, in which he is letting Yuna know he is alive since he can't find her, and hopes she will find him in return.
The next day at Heian-ji, Koku and Keith meet up. There, Keith asks for Koku's name, and offers his own, even though he is aware Koku knows. Koku only wants to know Yuna's location, but Keith reassures him that if Koku is alive, so is Yuna. Instead, he starts with the phrase "Jaula Blanca Institute," and says everything started at the Jetblack. At the end of the 16th century, 13 fossilized skeletons were found in the ruins on top of a mountain. The scientists identified winged skeletons as progenitors of humanity and were essentially gods. Thus, there the project to resurrect these gods began. Since the king and government realized this project could have monetary value, they gathered donations under the pretext for resurrecting these gods and built the Jaula Blanca Royal Scientific Institute where many of the top researchers gathered to work on resurrecting the gods. However, some of the researchers were blinded by the money and became corrupt, spending days wasting away on different projects, specifically the inbreeding program which produced malformed, insane offspring, called the Promising Ones.
These were created again and again over the centuries and when rumors that the program would be shut down, one of the researchers, proposed to the king to create a program that would balance the kingdom's fear and tranquility inside and outside the kingdom. Thus, the Promising Ones became part of an elite government agency to maintain order and chaos, which is known now as Market Makers, allowing the facility to continue. It was after this program began that the progress on resurrecting the gods actually progressed. Two lives were born to show them the way of success, but something happened. From here, Koku remembers being in a burning building, looking for Yuna, his dead friends, and his signature B on a chalkboard. Koku asks Keith how he knows so much about him, and Keith reads a name next to 13 from a notebook saying, its written Kurohane, meaning black wings, but actually read as Koku.
The jetblack epitaph is then brought up by Keith, saying its on the top of Mt. Cremona. Through advances in genetic research and deciphering that inscription, their research was able to progress. The inscription contained a record of abilities and form of the god's bones. It was the help of three cellular biologists from Japan that led to the birth of Koku and his guardians. One of the three biologists was Dr. Kazama, Keith's father. Keith also reveals that the one who was able to decipher that inscription was himself, aged 12. At that moment, Koku feels the presence of someone watching over them, with intent to attack. Koku engages with the attacker, whom is wearing a mask. The fight gets intense and essentially destroys the temple, with Keith in awe of their powers. In the middle of the fight, Koku is able to knock off the mask and the attacker is revealed to be Yuna. Stunned, Koku refuses to fight and asks Yuna if she remembers him. She states that he is the reason all their friends are dead and stabs him in the stomach. Still, Koku begs her to remember him, and she is hit with memories of their younger selves. She remembers and asks Koku where he's been all this time and she's been waiting for him. At this moment, Minatsuki, whom was watching the fight stabs both, and removes Yuna from Koku.
In episode 7, Koku, desperate to take Yuna back, he tries to attack, however, Minatsuki has the upper hand and has air blimp above him shot down spears. Koku, is completely down, and is about to be taken by the Market Makers when Keith shows up with a shot gun and shots Minatsuki. Minastuki is actually harmed and is shocked that he could be harmed, as he was told only the black winged king could harm him. Lacia tells him to retreat for if he doesn't fix this as soon as possible, it would be irreversible. Thus, Koku and Keith are able to escape and Keith remembers what his father said about Koku being drawn to Keith because of his relation to Dr. Kazama and to guide Koku well. As this all happens, a flashback of Koku's past reveals what happened on that day. It is of him and Yuna when they were younger, surrounded by other children. Three boys gather around Yuna and begin to tease her, prompting Koku to show up and tell them to leave her alone. As they tease Koku for always showing p for Yuna, they also push him down. However, he is still brought into the building by them, signifying that they do still care about Koku and do not just mercilessly attack him. Koku wonders why he belongs in this institute when he is not strong like the other kids and can't even use his left eye on people. Dr. Kazama tells him he does belong, but Koku doesn't understand. Then, Yuna and Koku are talking by the river, a distance away from the institute and Yuna thanks him for protecting him. She's also aware that if they're seen talking again, the other kids would tease him, so that's why she brought him out so far, and says that she would also protect him. The two of them come up with a sign that they would draw whenever they needed help, so the other would know to come. This is the origin story of the B sign that is left by Killer B, in which B is 13 and the four slashes is four in roman numeral.
Soon after, their institute is attacked by soldiers, Koku instantly runs to Yuna's room to look for her. Dr. Kazame watches and tells Kirisame, to take Koku to somewhere in the woods instead of the shelter because Koku must be protected. Kirisame listens and takes Koku away, while telling him Yuna will be alright. Instead, Yuna is actually in a classroom, with their sign drawn on the blackboard, waiting for Koku. Yuna is approached by two children, Minatsuki who is claiming to be Koku's older brother and Izanami. Minatsuki tells her that Koku is waiting and leads her away, as Izanami looks on slightly suspiciously. The two children are then found by Dr. Kazame who is grateful that they are still okay and warns them to go. However, they are cornered by soldiers and then Minatsuki stabs Dr. Kazame, claiming to never be his spare parts and sides with the soldiers. As Dr. Kazame falls, he begs Minatsuki to not listen to "him," a mysterious person leading the soldiers. As Koku and Kirisame run towards the tree shelter, the soldiers arrive and start shooting at them.
Kirisame tells Koku to go into the tree and lock it and that he will be right behind. Kirisame's arm turns into a blue steel sword as he goes to face his attackers. Other children soon arrive and also begin to attack the soldiers. When Koku finally leaves the tree shelter, all the children are dead, and he runs back to the institute. He sees the sign Yuna left for him in the blackboard and is crushed he missed her. He then finds Dr. Kazama as he is dying of his wound from Minatsuki, and he gives Koku a slip of paper that would tell him what to do. With set instructions he returns to his dead friends and begins to saw off Kirisame's arm, resulting in his own arm.
In present day, Koku is sheltered by Keith, also on the run as he is the suspect in the death of Jean Henri Richard. Badly injured, Koku talks to Keith about his past, and that his left eye has the ability to alter memories. Since he was told to never use it on anyone, Koku used it on himself, when he no longer wanted to remember the memories of back then.
In episode 8, Keith and Koku discuss their current situation. Keith says he saved Koku because he still has things to ask him. Keith reveals that his sister was murdered a long time ago, and someone named Dead Kyle was the one they thought was the killer. Dead Kyle admitted to the murder and was arrested for the crime. However, while he was in the mental hospital, he escaped, and whilst in the middle of committing new crimes, he was killed by a third party. Keith wants Koku to tell him about Dead Kyle, about why he admitted to a crime he never committed, and who he was covering. Koku tells Keith, Dead Kyle was a released Reggie (Regulus Ginedrive Immoral Egersis), meaning he was not human. Koku tells him Reggies are essentially ancient demihumans created solely to fight and that Dead Kyle was one of the Reggies that attacked the institute that day. Koku admits that he killed him, and Keith is not surprised to know that Killer B's motive this whole time was revenge and concludes that everyone killed was a Reggie involved in the attack on the institute. Koku swears to continue his revenge campaign until he finds Yuna. Keith also tells Koku that the Market Makers also sometimes manipulate humans to do their biding.
As the two of them continue their fugitive run, they discuss the presence of Reggies in society. Reggies go insane after a certain age and are usually discarded, but can be returned to "normal" with the gold solution, which adjusts their testosterone and dopamine. Koku tells him there are more than you think residing in the you would expect. Koku also states that the only way to stop Reggies is to kill them because they are essentially weapons and do not stop.
At their new hide out, Koku and Keith's conversation continues. Keith is aware that blue steel is the weakness of Reggies because of his father's notebook. Koku is impatient about just hiding and wants to do something, but Keith says they will wait until Koku is back to full health. When Koku proves he is, Keith gives him his theories on who is behind all this. He says he has been studying two men, which is why he came back in the field but is constantly stumped by two assumptions that seem unrealistic. One is the existence of non-humans and the other is an ability to bend and change people's will. Koku the realizes, Yuna is not the same Yuna she was before, and was probably controlled by Man One, and has the same ability as himself, concluding that they are probably related. This Man One is also the one that continually tries to capture Koku. When Koku asks about Man Two, Keith tells him its unrelated to him. Keith wonders why Man Two is partners with Man One instead of Man One controlling him with his ability and comes to the conclusion that Man Two is immune to the ability and has his suspicions on who it is. Koku is convinced and agrees to help. Keith tells him that their base is in the skies, near Canopus just as they are caught by Lily who has been tracking them this whole time.
The three of them return to Keith and Koku's hideout and tries to hide their relation to each other. However, they are soon under attack by Takeru, who was sent to scout them out.
The next episode begins with Keith and Lily ducking from the bullet wounds as Koku changes his arm into a sword in front of Lily. Keith tells her to watch closely as Koku flies towards Takeru and easily kills her. Keith decides to part ways with Koku and follows Lily back to the RIS to get interrogated but also begin his attack on Man Two.
Episode 10 begins with Koku on top of a snowy cliff and thinks back to his conversation with Keith when they were still together. Keith tells him how he can fly to Moby Dick, a white ship in the skies, by following the route of a specific bird, by jumping off a specific cliff at a specific speed to catch a updraft and to ride it up. Keith hypothesis that that ship is where Yuna will be because that is the Market Maker's base, and believes she is still alive even after that stab wound because of the inscriptions. Keith says he was the one that translated it and because of that the one story that stood out to him was "The Tale of Two Shrine Maidens," in which on the 13th, a man was chosen by two shrine maidens to receive power, companions, and wings and became the black winged king. They also granted him a steel that burned blue. Afterwards, they told him to decapitate one of them, and her power would merge with him. In this situation, Izanami gave him her power after he killed her. The other would rule with him and share the same fate. Koku, upset that Yuna would eventually share the same fate as him is upset, but Keith tells him to fight against fate. Koku sits on the cliff preparing his flight.
In episode 11, he is seen flying towards Moby Dick. Onboard Moby Dick, Minastuki is becoming more unhinged as he attacks Yuna, who believes that Koku will come for her. Lacia is seen walking towards Minastuki with a gold solution needle, but decides not to relieve him of the madness and to use him as a distraction to escape with Yuna. When Koku is close enough, both him and Yuna's hair turn white. When Minastuki and Koku meet, Minastuki is completely insane, not remembering who he is and wildly attacks Koku. Koku easily defeats him and wanders the airship looking for others. However, Lacia and an unconscious Yuna have escaped by helicopter and blows up the ship, breaking Koku's sword arm.
Lacia awaits for Koku at jetblack with Yuna tied up. Keith warns Koku to not go to jetblack as that is the only place where his regenerative skills do not work. Still, Koku goes to save Yuna. While waiting for Koku, Lacia tells Yuna of his obsession with black and that is is perfect because it is created by mixing all the colors together. Lacia reveals that he was often alone and wondered why he was kept isolated until Izanami came along. It wasn't until that night when the Reggies attacked that he learned the "truth", that he was just spare parts for Koku. However, in reality, it was because he was a "perfect Reggie" that successfully survived stabilization and was immune to Koku's eye, meaning he was a threat to the military. Thus, that night, the Reggies actually attacked because of Lacia, who is actually Minastuki. Lacia controlled another Reggie to make that other Reggie believe he was Minastuki and run his plans while he himself, hid in the shadows. He has aspirations to become the black winged king, and must kill Koku to achieve that dream. When Yuna disagrees, he stabs her, but refuses to kill her until she watches Koku die.
In the final episode, episode 12, Koku arrives at the jetblack and begins to fight Minastuki, who takes advantage of Koku's inability to regenerate by shooting him and stabbing him as Koku's body is not in peak condition. Finally, Minastuki torments Koku by telling him after he digs out Koku's eye, Koku can join his other friends in heaven. However, Koku disagrees, saying all his friends are with him, inside, as he is living for him. Agitated, Minastuki goes to pull the knife he stabbed in Yuna, resulting in massive blood loss. Koku surprise attacks Minastuki one last time and uses Izanami's sword leg to cut Minastuki's head off. Afterwards, Koku leaves jetblack with Yuna in his arms.
In the epilogue, Koku and Yuna lives with Keith, and when Lily comes to pick Keith up for the first day back on work, she looks for the two of them. When told they left, she accepts and hustles Keith into her car so they can head to work. As they talk, she sees them on the street out of the corner of her eye and makes a sharp u-turn and offers them a ride, willing to ditch work to hang out with them. While Yuna agrees, Keith and Koku states there is no space in Lily's two seater and refuses.
The kanji in Koku's name are black (黒) and feather (羽).