Koshirō Chikuma (筑摩 小四郎, Chikuma Koshirō) is a member of the Iga Tsubagakure clan and one of the ten ninja picked by Ogen to participate in the battle against the Kouga. He is Oboro's childhood friend and Tenzen's apprentice.


Koshirou Mask

Koshirō with his mask

Koshirō is a young man with long, messy black hair and rather bushy eyebrows. He also has two small scars at the bottom of his left cheek; how he got them, however, is unknown. He wears a black, sleeveless kosode with a netted shirt underneath and black hakama which are tucked into his socks. He wears a traditional pair of sandals like many of the other characters.

When he is blinded by Gennosuke he wears a black mask which covers the upper half of his face. The mask has a large red kanji character painted on the front, which is not translated by any of the characters through the course of the series. Not only is this aspect incoporated into his character, but it is even notable that he develops slight facial hair. Also, though it is only when he is on the ferry, Koshirō wears a long, dark kosode which hangs over his shoulders. Assumingly, he may have wore this to give himself an overall less approachable appearance.


Before the WarEdit

Not much is known about Koshirō before the war except that he has been friends with Oboro since they were children and he was chosen by Tenzen at some point to be his appentice. He is seen outside Ogen's room with Jousuke Udono when Oboro and Gennosuke were having their first meeting together. Jousuke attempts to strike up a conversation with him but Koshirō simply gives him a cold stare, putting an end to any attempt at small talk. When Oboro falls over and screams he immediately runs to Oboro's aid, giving Jousuke another stare as a warning to stay outside.

Despite his ranking of Genin (a ninja footsoldier) in the Iga hierarchy his extreme talent is noticed by even Ogen, who chooses him to be one of the ten to represent Iga in the war with the Kouga.

Battle with ShougenEdit

Koshirō is first seen sitting by Tenzen's side when a group of Iga show him the scroll. Upon hearing of Ogen's death he appears to be slightly upset, but quickly puts it behind him and focuses on the opportunity to kill the Kouga. Tenzen realises that Shougen Kazamachi will be carrying a similar scroll back to Kouga and, after sending Jingorou back to Iga, leads the group out to kill him.

The route to Shougen's location the group comes a traveling carriage containing a Kouga ninja. Under Tenzen's orders Koshirō uses his Kama scythes to kill the two carriers, bringing the carriage to a halt. The group open it up and find Juubei Jimushi, whose snake-like body startles them all significantly. Tenzen confidently tells the others to go ahead, waiting behind to finish off Jimushi. That night the group finds Shougen and leap down from the trees to attack. Koshirō attempts to use Kamaitachi but Shougen spits his glue-like saliva at him, sealing his mouth shut. Shougen takes position on a tree and when Koshirō, Nenki and Rousai rush at him he spits out his saliva through his teeth, catching all three in a large web. The group are saved by Hotarubi, who summons her butterflies from the sideline and distracts him from killing them. She then throws Nenki one of Koshirō's dropped Kama and Nenki uses his hair to embed it in Shougen's forehead before slicing through the web. As Shougen falls he throws the scroll into the darkness where it is caught by Jimushi. Koshirō rips off the saliva and chases Jimushi with Nenki and Rousai.

The group are unable to catch up with him but Tenzen eventually appears before Jimushi and slices him in half. The group then light a fire and compare the scrolls and when they see they are identical Tenzen orders Koshirō to throw the Kouga's in the fire. As the group watches it burn Hotarubi silently emerges from the woods and tells them Shougen is dead. The group are happy to learn of this news and set their sights on their next victims.

Attack on the KougaEdit

The next day the group head towards Manjidani under the guise of bringing a message from Gennosuke. Koshirō and Rousai eliminate the guard posted in one of the trees, allowing them easy access directly into the village. Once inside the group discuss killing the remaining Kouga ten but Koshirō suddenly senses a presence nearby. The five ninja begin to scout the area when Rousai is dragged off, getting slammed into the wall. The others are stunned and make no attempts to help him, leaving hi to free himself. He escapes and warns the group the wall had spoken to him. Before the Iga could do anything the wall shouted for reinforcements and they became surrounded by Kouga ninja. Once Tenzen's attempt to talk them down fails Koshirō rushes straight into battle, slashing at the ninja surrounding him. He is attacked by a ninja with a similar appearance to Shougen but this time Koshirō is prepared to deal with him. He dodges the ninja's adhesive saliva and uses his scythes to slice through his opponent's arms. The injured ninja tries to use his saliva again but Koshirō uses his Kamaitachi technique to absorb it before using the same technique to decapitate the spider-like ninja. At this point Gyoubu Kasumi emerges from the wall he had hidden in to confront the Iga.

The five ninja re-group to face Gyoubu when they are interrupted by the arrival of Hyouma Muroga, Saemon Kisaragi and Kagerou. Tenzen explains the group's actions as being self-defense and throws a shuriken which had been embedded in his scabbard at Hyouma. Kagerou blocks the attack but the Kouga are unable to stop Hotarubi summoning a swarm of butterflies, into which the five Iga disappear.

Return to IgaEdit

The Iga immediately set off for Tsubagakure to meet up with the others but come across a young woman. Tenzen speaks to her politely yet suspiciously, which the woman realizes and so she speaks back to him in a rude manner. Koshirō is unnerved by this, grabbing hold of one of his Kama sycthes to attack, but is stopped by Tenzen. He introduced himself to the woman, and she does the same; they learn that her name is Okoi. When Tenzen realizes that her name is on the scroll, he immediately attempts to convince her to travel with them to Iga. However, she refuses Nenki chases her down and knocks her unconscious, keeping her a prisoner under Tenzen's orders.

Once they reach Iga Tenzen orders a meeting and the group heads to meet up with Akeginu and Jingorou to discuss the events that occurred, however both Hotarubi and Koshirō are absent from the meeting. Koshirō is later seen with Akeginu waiting outside Oboro's room while Tenzen tells her of the peace treaty being broken. Oboro doesn't take the news well and immediately runs to the storehouse where Okoi is being held, followed closely behind by Tenzen, Koshirō and Akeginu. At the storehouse the group run into Yashamaru, who doubles over in pain at the sight of Oboro. It becomes apparent that it was Saemon who had been in disguise. Having been discovered he throws his sword at Oboro, which is quickly blocked by Tenzen. However Tenzen accidently knocks Oboro backwards and Koshirō immediately leaps forward to catch her, missing his opportunity to catch the scroll Saemon had thrown. He realises he had grabbed Oboro inappropriately in the fall and quickly lets go, clearly embarrassed, before chasing after the scroll, now held by Gyoubu. The group chase Gyoubu until he seems to disappear at which point they head to Gennosuke's room.

Upon their arrival they see that Gyoubu has given the scroll to Gennosuke. Nenki orders an attack but the group of nija that attack all begin to kill each other or themselves unders Gennosuke's Dojutsu skill. The remaining Iga part to allow Gennosuke, Gyoubu and Saemon to leave except for Koshirō. He appears behind
Koshirou blinded

Koshirō's Kamaitachi turns against him

Gennosuke and tosses a scythe which is blocked by Saemon. He then begins to use his Kamaitachi skill but is interrupted by Oboro appearing, telling them to stop. Tenzen tells her to use her skill to nullify Gennosuke's Dojutsu but Oboro is unsure of what to do and Koshirō again tries to use his Kamaitachi skill only to have Oboro jump in front of him and get in the way of his attack. Koshirō attempts to cover his face and look away from Gennosuke but he is unable to and he uses Kamaitachi on himself, completely destroying his eyes. Koshirō collap
Koshirou injured

Koshirō lives but is blinded

ses to the ground in a fountain of blood while the Kouga make their escape with Oboro crying for both him and Gennosuke.

Koshirō is quickly taken away by Akeginu who bandages and tends to his wounds. He is seen in his room in obvious pain with wrap covering the upper portion of his face. While Akeginu is able to keep him alive she is unable to save his eyesight.

Assassination on GennosukeEdit

While Koshirō is being looked after in another room the Iga learn of the Kouga's whereabouts and Tenzen sends Hotarubi and Nenki to trace them. The next day Koshirō travels with the others to a small inn where they wait for Hotarubi and Nenki to return. That night Koshirō, now wearing a mask that covers most of his face, heads outside in the rain to be by himself and get used to being blind. He remembers back to the night before and wonders if Gennosuke is a monster. Suddenly he senses
Akeginu and Koshirou - Rain

Akeginu comforts Koshirō

a presence behind him and he begins to panic, imagining it is one of the remaining Iga creeping up behind him. Frightened, he spins around with his kama scythe in hand and pins down the approaching presence. He then hears Akeginu's voice; she calls out his name and then asks what has happened to him. Realizing what he has done, he quickly leaps backwards to get off her. However, he lands awkwardly and falls backwards into a shallow river, where he breaks down and admits that he is now useless. In obvious mental pain, he bites his lower lips until it bleeds. Akeginu notices this and lifts him up so he is no longer lying down in the water. In order to comfort him she wraps her arms around his head and holds him close, sheltering him from the rain.

Some time later, after the two of them leave the river, they are both seen sitting on individual rocks with the rain still pouring down on them. They sit in silence until Akeginu finally says they should head back to the inn. She stands up, as well as Koshirō at the suggestion, however she says it would be wise for them to leave separately. Koshirō queitly agrees and politely takes a seat once more. As Akeginu takes her leave, Gennosuke's flute falls from her sleeve and onto the ground. When she realizes this, Koshirō asks her if something is wrong, however she tells him nothing is as she retrieves the fallen item. Akeginu then suddenly asks Koshirō how he feels about Oboro; however, before he can answer, she explains that Oboro must kill Gennosuke, and further explains how she feels for her yet pities her. She then says that it is her wish for Oboro to forget about Gennosuke, but does not believe she is capable of this. Koshirō agrees with her and then goes on to say how he thought he knew every expression on Oboro's face, but when she was with Gennosuke she had changed in a way he could not describe. He suddenly stops talking, taken over by his emotions. Akeginu says his name as if to ask him what it wrong, however he begins to speak once more. Putting his hand to his face, he says that because of what Gennosuke has done to him he will never get to see Oboro again.

Ferry Ride to SunpuEdit

The next day, the remaining five Iga board a boat to ensure a quicker method of travel. Koshirō is seen sitting quietly beside most of his clansmen, while Oboro is alone by the railing, thinking to herself when the boat sets off. The waves that bump against the boat are strong enough to cause her to lose her balance; she falls backwards
Koshirou catches Oboro

Koshirō catches Oboro

but is caught by Koshirō, who tells her to be more careful. She thanks him, placing her hand on his to express her gratitude. Koshirō seems to be shocked by this and turns his head aside. The two of them sit together unmoving until Akeginu's voice can be heard calling Oboro's name. Koshirō quickly lets go of Oboro and is able to distance himself from her before Akeginu can see them. Koshirō listens as she walks over to Oboro, telling to she should join the others inside as she offers to help her up. However, Oboro denies her request, saying she rather stay outside because she wants to experience everything the ocean has to offer. Suddenly the traveling minstrels on the boat begin to play, which remind her of Gennosuke. She says his name, which seems to disheart Akeginu. It is the same with Koshirō, who puts his head down before standing up to take his leave with Akeginu watching him go.

Later, Koshirō is sitting by the main cabin under Tenzen's orders. To pass the time, he begins carving a statue from a small block of wood. Two passengers unknowingly approach him, speaking fondly of the traveling minstrels performance earlier, saying they should offer them some of their wine. However, the two men stop talking when they finally realize Koshirō sitting ahead of them; they are quickly frightened by his appearance and slowly back away. Alone once more, Koshirō continues carving the wood. By this point it is nearly complete and its expertly crafted appearance is that of Buddha. He rubs a finger against the face and then bites his lower lip.

While Koshirō finishes carving the Buddha statue, a young boy watches him as he works. Finally realizing this, he stops what he is doing and lifts his head as if to look at the boy. The child merely smiles and apologizes for staring, and then comments on his work. He is confused when Koshirō puts the Buddha statue aside to
Koshirou and young passenger

Boy watches Koshirō carve

begin working on something else, but continues observing anyway. Suddenly the boy's father hurries over to apologize to Koshirō about his son's curiosity. The two go to leave when Koshirō holds out his hand. Noticing this, the boy runs back to him and is given a small wooden frog. He wholeheartedly thanks Koshirō before going back inside the cabin with his father. When they are gone, Koshirō strokes the face of the Buddha statue before working on it once more.

From inside the main cabin where Oboro and Tenzen are, there is a scream. The suddenness of the noise frightens Koshirō and causes him to cut his finger with his knife and drop the Buddha statue. Being so close to the entrance of the cabin he is apparently the only person who can hear Oboro screaming from within, crying out for help. He quickly realizes that Tenzen is trying to take her for himself. In his head, he begins to plea for Tenzen to stop what he is doing. Out of confusion and anxiety he begins breathing out, creating small whirlwinds which catch the attention of some of the other passengers on the boat. While Oboro continues to scream, Koshirō begins to argue with himself if he should save Oboro or let Tenzen have her. He considers helping her, but knows he cannot defy his master; at the same time he realizes Tenzen is attempting to crush everything she believes in for his own selfish goal. He begins apologizing in his mind, admitting he does not know what to do as Oboro cries out for help from her other clansmen. He covers his ears in an attempt to block out her voice, but then thinks of her adoringly saying his name in his head until he hears her actually screaming it. The pressure becomes too much to bear and Koshirō frantically crawls to the main cabin in an act of desperation. At the entrance, he yells out for his master to cease his actions, but stops when he hears Tenzen fall to the floor. Oboro says Koshirō's name, and then tells him what Tenzen was attempting to do to her. Confused with the situation, Koshirō touches Tenzen's body only to figure out that he is dead. Slight anger in his voice, he asks if Oboro did this to him, to which she says she thought Koshirō is the one who stopped him. Confused, the two of them sit in silence.


Of all the characters in Basilisk, Koshirō differs the most between the original manga and the anime. In the manga, Koshirō shares Tenzen's sheer ruthlessness and arrogance in combat while the anime depicts him as being more reluctant to fight any battle where his opponents would suffer an overwhelming disadvantage, prompting Tenzen to lecture him on how chivalry has no place in a war between ninja. He is very loyal in both versions and becomes extremely conflicted in who he should side with when Tenzen attempts to rape Oboro.

In the anime, Koshirō is an expert woodcarver and after being blinded quickly learns to carve with equal skill using his sense of touch alone. He also has an odd tendency of biting his lower lip until the point of bleeding.


Kamaitachi: Koshirō's Kamaitachi technique allows him to create miniature vacuums when he breathes, which suck his enemies in and then shreds them to pieces. These vacuums are extremely powerful and are able to completely rip off an opponent's head, though aren't always fatal as he survives when Gennosuke turns the attack on himself.
Koshirou - Kama Scythes

Koshirō with his Kama scythes

Kamajutsu: Koshirō wields a pair of Kama scythes which he can use in close-range combat or throw like boomerangs. He has near-perfect accuracy when throwing the Kama, able to target specific people he wants to hit and even hit fast-moving targets.

Enhanced Senses: After being blinded by Gennosuke his other senses adapt to compensate, although he's nowhere near as capable with his blindness as Hyouma Muroga. An example of this is when he mistakes Akeginu for an enemy and goes to attack her, only to back off when he hears her voice. His inability to get used to being blind later affects his effectiveness in battle, eventually leading to his inevitable death.


Tenzen YakushijiEdit

Tenzen is Koshirō's teacher and Koshirō is completely loyal to him. As Tenzen's apprentice he believes he's obligated to follow his sensei's orders regardless of how he personally feels. This causes him to struggle to come to a decision on whether or not to save Oboro from him


Koshirō and Oboro grew up together and despite the difference in their stations she sees him almost as an older brother. Koshirō himself is completely devoted to Oboro and may even hold romantic feelings for her.


Koshirō has a rather close relationship with Oboro's bodyguard and confidant but is almost completely oblivious to the romantic feelings she has towards him. He seems completely dumbfounded when Kagerou, disguised as Akeginu, confesses her love to him. Despite this, he still allows her to kiss him, only resisting when he briefly thinks of Oboro.

Differences between the Manga, Anime and Novel VersionsEdit

Koshirō's manga self doesn't seem to have any apparent romantic feelings for Oboro. He still cares for her deeply (despite still trying to assassinate Gennosuke behind her back), yet those feelings are kept mostly as platonic friendship or lord/lady respect. Koshirō is also the centerpiece of several scenes in the anime that never occurred in the original manga, like his encounter with a little child whose father would be sacrificed by Tenzen during his fight with Gyoubu Kasumi.

Koshirō in the novel is more similar to the manga than the anime. His feelings for Akeginu is that of a younger brother, so he remains unaware of her more romantic sentiment. Like the anime and manga, he is Tenzen's student/servant (Tenzen having trained him ever since he was a child) but he still tries to stop Tenzen from raping Oboro. Like the manga and anime, he never gets quite used to being blind. Instead of two hand scythes, Koshirō in the novel wields one large two handed scythe that's far too heavy to be thrown but is much better suited for close range combat.

Appearance in Other MediaEdit

Koshirou Movie

Mitsuki Koga as Koshirō

Koshirō was included in the live-action movie Shinobi: Heart Under Blade played by Mitsuki Koga, although several changes were made to his character. The biggest was that Koshirō was part of the Kouga ninjas, had a beard and did not use either sickles or his kamaitachi technique. Instead he wields shuriken and a pair of kunai attached to chains. He is also able to project hundreds of wooden spikes at a time, making him the best weapons user in the movie. He eventually grows frustrated at Gennosuke's unwillingness to fight, and leaves the group to fight the Iga ninjas by himself. He manges to kill Hotarubi but is forced to retreat on horseback after being injured by Tenzen. He is chased and killed by Oboro in revenge.


  • Koshirō's name can be translated to "wide-minded" or "ambitious".
  • In the manga, when Koshirō wears his mask, there appears to be blood stains where his eyes would be.
  • In the anime, his eyes appear to be brown; however, later on when he is blinded, whenever his face is shown he appears to have blue eyes instead.


  • (To Akeginu, about Oboro) "Thanks to him I will never have to see her. I will never have to see her getting drenched by the rain."
  • (To himself) "Gennosuke, I do not doubt the love you feel for Oboro-sama. But how can you be satisfied with the nightmare we are putting her through? You are nothing but a Kouga. If the Kouga were dead, my princess wouldn't have to endure such pain."
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