Senzui was one of the two masters of Kajima Satomi and the current head of the Kuremisago Clan. He appears to be the true leader of Yami and the One Shadow Nine Fists, as he was masquerading himself to be Saiga Fūrinji the entire time, and as "Saiga" was one of the real masterminds behind the rebirth of the Eternal Sunset.
Senzui is a fairly tall and slim man, his physique is similar to Saiga, being very well muscled. Senzui has medium long black hair that falls to his back and stands erect on the sides of his head. He dons what appears to be an ancient-like long sleeve shirt with a sash tied across his waist, under his shirt is a chain-mail vest which supports his ninja appearance (similar to Shigure and Kenichi). Senzui also wears gauntlet bands around his arms and legs with soft ninja shoes.
Senzui is a very cunning and manipulative man. He was the mastermind behind the Eternal Sunset operation all along, meanwhile impersonating Saiga Fūrinji, willing to make everyone believe that all his actions were Saiga's, even putting Miu (Saiga's daughter) against him, forcing her to believe that Saiga was Shizuha's (Saiga's wife) killer.
His most important quality is his indifference and merciless attitude towards innocent people, having claimed he does not have any remorse or mercy in killing anyone in order to fulfill Eternal Sunset plan, claiming that the plan is top priority over everything else (even the human life). This even extends to his own disciple Kajima, as after the latter used a forbidden move solely to advance martial arts and cost him his left eye, Senzui expressed little remorse and refused to let Saiga help him.
However, Senzui wasn't always a ruthless man. As during the war with the Kuremisago and the Liberationists Senzui still maintained some of the Katsujinken beliefs along side his former friend Saiga. However, with the number of lives being lost on the battlefield left him to believe that the war would never end. To that end, he was influenced by the elders of his clan and ruthlessly murdered his own people to cause discourage on both sides while disguised as Saiga to ensure he wouldn't lose face to the public and label Saiga as the culprit to reafirm the clans beliefs. To that end, his lack of morality on life is further extended during the Eternal Sunset as he was more than willing to bomb numerous countries while exhibiting a hypocritical nature stating it was all for "peace". Also, according to Saiga Senzui didn’t want the Eternal Sunset to happen and it was due to Mikumo Kushinada influence that he started to plan for it.
Due to his Kuremisago heritage, he believes that emotions on the battlefield or in martial arts are useless. This extends in battle as well, as when he murdered his father (albeit indirectly) he expressed little remorse. However, he was shocked by the deed somewhat.
He even stated that all of his actions like the killing of Saiga's wife and attempt of his daughter was merely a compensation for Saiga's mistakes. Despite his beliefs about emotion in martial arts being useless, he still showed some level of remorse (albeit very little in amount). Even after killing Shizuha, the woman that he loved, he could't killed Miu as a baby and left her alone in the snow, shedding a single tear by the atrocious act that he just committed.
Senzui was born the leader of the Kuremisago clan. He was designated by the clan to marry Shizuha. One day however he met Saiga Fūrinji and, despite their initial quarrel, they became friends and even rivals who trained on a daily basis. He also approved of Saiga marrying Shizua while most opposed of it due to him being an outsider.
After Saiga and Shizuha Fūrinji tried to ask for her hand in marriage the most conservative people (Senzui supported the union) opposed to it while some others turned over Saiga and Shizuha's side in order for a new way of life. That forced into a feud driving the clan into two sides that eventually fought bloody battles around the world, one which resulted in Senzui (albeit indirectly) killing his own father. After many battles caused many Kuremisago members to pass away and Senzui to do something to Saiga and asks for Saiga's forgiveness for what he is about to do.
With that, Senzui, while disguised as Saiga began killing off many Kuremisago members in an effort to stop the fighting on both sides. He is commended by an elder for his cold-bloodedness in killing his comrades and is reminded to stick to his promise so that the traditionalists will reach a compromise with the liberal faction and end the fighting. Another elder states that Senzui will be made one of the elders of the Kuremisago after the fighting but he says that he does not matter to him, as he only wishes the fighting to end with the least amount of casualties. He is then ordered to carry out his goal to the end, and for that he needs to kill Shizuha and her child.
At some point after that, Senzui killed Shizuha while pretending to be Saiga plus marking baby Miu memories making her belive that Saiga was the one who killed her mother. He choose to leave Miu alone out of respect towards Saiga and his love of Shizuha. Then some time later joined Yami and became the One Shadow of the One Shadow Of The Nine Fists as well as one of the rulers of the organization itself. He then became the master of Kajima Satomi along side Saiga who, at the time, was unaware that Senzui murdered his wife.
Senzui (while disguised as Saiga) is seen along side all of the remaining Yami members greeting Seitarō Raigō and the rest of the Hachiō Executioner Blade members. Saiga stated that this is all for the sake of the Eternal Sun. He and the other masters ride in a helicopter to the building of their destination and are later surrounded by the masters of Ryozanpaku (minus Shigure and the elder) while Saiga comments on them being there. As Akisame questions if he will say anything since meeting them in ages, Saiga remains quiet. When the Ryozanpaku masters work together in sync, Saiga comments on their power. However, once the masters noticed they have no killing intent and hearing of an incident at the port, they realize it was all a diversion.
Once in the conference room with the Prime Minister, the minister notes how they've grown greatly and how powerful they are, but asks if he may stop his attack at the harbor. When the minister asks if they can reach a diplomacy, Saiga states that he is under the wrong impression. He states they did not come to negotiate, but to make an announcement that the fleeting days of citizens will come to an end today. When the Prime Minister questions what he intends to do to the country, Saiga corrects him stating it's the whole world and declares the Eternal Setting Sun.
Afterwards, he attempts to leave, but Sakaki refuses to let him. He asks if that is a good idea since 7 of the Hachio Executioner Blade members are on the ship with Shigure right now. As Ryozanpaku leave, Akisame questions his response, stating there is a high chance Miu is on that ship. Saiga responds that since she is of his blood then she will handle if with her own power. Akisame criticizes him, stating that's not what the man who went to Tidat to save her and instead Saiga would instead risk his life to save her. However, Akisame questions if he's instead gambling that "the man who you recognized and allowed to use your tekkou" to protect Miu, Saiga smiles and agrees before walking away.
Afterwards he communicates with Akira that he and Michael have taken the base that they were assigned to take. Later on he was watching the missions of the teams of One Shadow Nine Fists with the Members of Hachio Executioner Blade.
Later as Yami's fleet of ships is on the move to intercept the world alliance's forces as Saiga Fūrinji looks on. An officer reports that despite the large force of the world alliance, Yami's control of the satellites prevent them from getting information about Yami's movements. Saiga states that the enemy's uncertainty will lead to distrust and fear, plunging the world in the Eternal Sunset. A soldier from Yami reports that an airplane has bypassed their primary defenses and is approaching at high speeds. Saiga feels that Ryozanpaku is approaching and a fleet of airplanes is seen charging towards the island. Knowing of his former allies coming to save Shigure, Saiga merely comments that no matter the time, wars will be started by people and settled by people themselves and tells Seitaro that they are now in the Third Great War. Once he gets word of Ryozanpaku easily defeating the military, Saiga expresses little surprise, noting the only way to defeat masters is with other masters.
He then receives a call from Mikumo as Saiga is seen watching leaders of various countries arguing with each other about the current state of events and he tells her that it is almost time. He later comments that Mikumo is having a hard time fighting as one of his commanders orders ships to bombard the masters.
Later when Niijima try to sneak into the command room, he is stopped by Saiga who tells him to hand over the virus. After seeing that Niijima is trying to trick him he decided to kill him only to be stopped by Hongo. However, Saiga is not surprised by this and tells Akira that he knew that he would rebel against them.
Hongo stands off against the leader of One Shadow Nine Fists and the two masters exchange a series of blows. Saiga mocks Hongo's actions to protect Niijima as futile and Hongo lands a thrust on Saiga though he catches the attack between his fingers. Hongo remarks that even though it's their first time exchanging blows he can feel the darkness within Saiga. Saiga is surprised when is suddenly surrounded by Hongo on all sides and observes that Hongo intends to use both truth and lies to block Saiga's escape, choosing Saiga to determine where the real attack will come from based only on luck. Saiga responds by using a similar technique and the two masters clash. Saiga dodges past Hongo and comments that he was able to protect all of his vital points but Saiga was able to win the battle of luck, as a rain of attacks lands on Hongo.
Hongo survives the attack but is unable to move, as Saiga also hit the karate master's pressure point. Saiga does not kill Hongo as he believes they will eventually come to an understanding and he makes his way to kill Niijima. Niijima is helpless as Saiga reaches out to kill him but is saved by James Shiba who was directed there by Kenichi. However, Shiba says that he did not arrive to save Niijima but rather to settle his grudge against Saiga as Saiga calmly comments that the forgotten underground boxer will die a pointless death.Saiga charges towards Shiba but the boxing master moves back and suddenly grabs Niijima. Saiga is caught off-guard as he realizes that Shiba is taking Niijima to escape. Shiba jumps 20 floors to take Niijima to the missile control room and he laughs at Saiga, saying that he intends to get back at him any way that he can, adding that revenge is about stopping your opponent's goals rather than defeating them in a fight. Shiba drops off Niijima and tells him to go on ahead as he holds back Saiga, destroying the entrance to the hallyway to prevent pursuit. Saiga arrives and mocks Shiba's attempt at buying time as the two masters prepare to fight.
The battle between James Shiba and Saiga Fūrinji (Senzui) seems to reach its conclusion, with Shiba inside a large crater pressed against the wall. Saiga calmly asks if the fight is over and turns away but Shiba regains his composure and charges towards Saiga, who blocks Shiba's punch with only two fingers and strikes back with a flurry of blows. Saiga compliments Shiba as his attack managed to graze Saiga's hair and he resumes communication with Mikumo. Saiga tells the missile control room to start the countdown and missile silos open as they prepare to launch a missile strike in ten minutes.
Just as Niijima prepares to upload the virus, Saiga arrives and sees that the control room has been breached. Shigure removes her sword so that the wall can close before Saiga reaches them and Saiga is seen focusing his ki onto his fist, as if to break down the wall. However, Saiga notices something behind him and sees Miu fighting with the Kuremisago disciples. Miu manages to defeat her opponents thanks to her mastery of her dou ki, though she is worn out from the fighting. She notices Saiga standing in front of her just as Kenichi and Kajima arrive, and Kenichi is launched against a wall from Kajima's attacks. Miu stands up to assist Kenichi and Kajima reports to Saiga and calls him "Ichiei-sama", making Miu realize that Saiga is her father. She walks towards Saiga (who tells Kajima to stand down) and he holds his daughter in his arms, then proclaims that he was the one who killed her mother. Kajima senses killing intent from Miu and restrains her just as Saiga dodges a kick from Miu. Kajima asks his master what he should do and Saiga answers that he would not give her special treatment, adding that anyone who gets in the way of their plans have to be killed.Okamoto, as he himself is as much a master of disguise as Senzui (as we saw earlier in the series when Saiga masqueraded as the overweight soldier in Tidat). Following up on the events described in the last paragraph: Miu eventually manages to make it past Kajima Satomi, and continues to attack the man who she thinks is her father Saiga, at which point Senzui in his disguise as Saiga attacks and is about to kill her. But at the last moment, the real Saiga, still disguised as Okamoto, shows up and rescues Miu. He and Senzui attack one another, ripping off each other's disguises in the process. Miu asks Saiga what is going on, at which point he tells Miu that they can talk later, but for now he must fight Senzui in order to avenge Miu's mother (thus revealing that Shizuha's true murderer was Senzui, not Saiga). He and Senzui then proceed to engage in a battle of truly epic proportions, both of them proving themselves to be Legendary Masters as they annihilate not only the fortified wall separating Shigure and Niijima from the action, but a huge portion of the building as well, with their first exchange of special-techniques.
Saiga charges towards Senzui with a barrage of punches, saying that he had trusted Senzui's judgment but he turned out to be Shizuha's killer. Senzui acknowledges that he lied to Saiga about his wife's death as Saiga's attack tears through an entire wall of the Yami base, but Senzui is unharmed and has caught Saiga's fist in his hand.
Senzui reminds Saiga that "a small sacrifice is needed for the greater good" and that it fell on Senzui to make that sacrifice as Saiga could not do it. Tears well up on Saiga's eyes as he reminds Senzui of his betrayal: to him, Shizuha, and the Kuremisago, but Senzui dismisses him saying that his actions saved the Kuremisago and ended the killing. Senzui proclaims that Yami will now let them experience true freedom, one you can only find within a fight. Saiga refuses to accept Senzui's solution and declares that he will not allow someone like Senzui to control the world. Saiga seeks to end their fight with his next attack and Senzui agrees to the challenge and the two masters unleash their ultimate techniques on a head-on attack.
After Kenichi's battle with Kajima results in his victory, Senzui and Saiga fall from above both covered in blood. Senzui notes there was a miscalculation in his results though Saiga notes he thought he'd die first but notes Senzui could fall over any minute. Saiga tells him to give up noting they both never wanted the Eternal Sunset to happen as he questions of Mikumo tempted him into this. Senzui ignores him and looks over Kajima noting how he never thought Kajima would only ever be defeated by someone who was blessed with talent and of noble blood only to have lost against someone who has no talent at all. He then recalls his past experience with the Kuremisago clan can only be free when the world is in chaos and reveals he has a remote detonator only for Saiga to reveal he stole it from him during their fight.
However, Michael Shtilvay arrives and, taking advantage of the situation, Senzui kicks Saiga causing him to drop the device as Senzui is able to recover the detonator. They land under the missle as Senzui notes if he detonates it now it will throw off the missle coarse. Saiga questions why he didn't kill Miu when he had the chance all those years ago to which Senzui replies he was careless, even though he was lying, the real reason was that he couldn't bring himself to kill the daughter who had the face of his best friend (Saiga) and the woman he loved (Shizuha). Saiga goes to attack him but Senzui activates the launch. As Saiga calls out to him Senzui stands on the pad Senzui, in his final moments, laughs stating he wins while remembering how he let Miu live due to his love of Shizuha.
The missile launches as Senzui dies from the extreme heat, however, the elder shows up and destroys the missile himself proving himself to be worthy of the "invincible superman" title once again..
Senzui is a very skilled master of the Kuremisago Style and the strongest member and head that the Kuremisago clan has ever produced. His combat prowess was able to easily defeat famous masters like James Shiba and Akira Hongo (although both fighters were in a handicap state of their own nature). Senzui is also a master of disguise as he was able to fool even a sharp mind like Akisame Koetsuji into believing he was Saiga for a while. His skills were able to overcome Shizuha's own power and skills. He is the best lineage within the Kuremisago.
- Master Ninja: As Senzui is stated to be the strongest member and head of the entire Kuremisago Clan, he is no doubt a powerful ninja and by extension assassin. This is evidenced in the fact Senzui was able to stealthily assassinate nine skilled members of the liberal faction when he was manipulated by the clan elders. Despite doing the assassination of the liberal members in the open and left their bodies to be discovered, nobody was able to suspect Senzui of being the perpetrator.
- Immense Strength: Senzui possesses enormous strength, capable of defeating a powerful S-rank boxer such as James Shiba (after having already fought Akira Hongo) with two fingers and seriously wound him with little effort. Just clashing with Saiga together resulting in a large steel cage door being smashed to pieces with nothing but raw strength. It was shown in the past that during Saiga's visit to the Kuremisago's village, Senzui was able to easily balance one end of an enormous boulder with just his index finger while Saiga balanced the other end. Later on in the flashbacks, Senzui's strength is enough to easily pierce and kill fellow clan members and ninjas of the Kuremisago Clan including very skilled ones despite the training they underwent made them powerful fighters.
- Disguise Master: Like Saiga, Senzui has great skills in disguises, such as how he disguised himself as Saiga Fūrinji and no one, not even anyone in Yami or the Hachio Executioner Blade knew of his true identity. The fact he was able to supress his ki around numerous high class masters, even a grand master of Mikumo Kushinada's level a testament to his amazing skills in supressing his ki. Even while fighting powerful masters such as Hongo and Shiba individually neither were able to tell the real from fake. In fact a testament to his disguise skills is the that he was able to trick even Shizuha Fūrinji into believing that he was Saiga despite the three of them being very intimate with one another with the latter two being husband and wife.
- Immense Speed: Senzui's speed is amazing, as he's capable of making numerous clones of himself against Hongo and even outclass him in every corner of their fight. Even a grand master of Saiga's level must keep his guard up just to be able to keep up with Senzui's speed.
- Immense Agility: Senzui is extremely agile where he was able to easily fight against Saiga in mid-air and had propelled himself on multiple surfaces of their surroundings to keep himself airborne with complete control over his movements.
- Immense Endurance: Senzui also has powerful durability as he continued fighting against Saiga despite receiving grievous injuries from the latter's techniques that were powerful enough to destroy their surroundings to hold on to the missile detonator.
- High Intellect: Senzui is a remarkably intelligent and cunning man, having been able to fool all of Yami into believing he is Saiga Fūrinji and even the elder, who is regarded as the Invincible Superman to believe that his son murdered Shizuha. Even Saiga commended his intelligence being far superior to his own.
Vs. His father (Won, Killed him)
Vs. Nine Liberal Faction Members (Won, Killed Them)
Vs. Shizuha Fūrinji (Won, killed her)
Vs. (presumed) James Shiba (Won, damaged his right eye and left leg)
Vs. Akira Hongō (Won)
Vs. James Shiba (Won)
Vs. Miu Fūrinji (Won)
Vs. Saiga Fūrinji (Lost)
- Senzui is the first Master class fighter that dies in the main storyline (no counting flashbacks) outside from a battle (the missile ignition). Shou Kano was the first character that dies outside from a battle.