Ensai Mukurou

About
Ensai is the founder and leader of the Noroi Faction, as well as serves as one of its Tetra Sealers. As such, his title is the Black Guardian. He is the only visibly inhuman member of the Tetra Sealers, as in a symbolic act where he gave his life to Noroi, he pierced himself with a katana in his chest, that is still here to this day. Because of this undead state, he continously sheds tears of blood.

Of the Tetra Sealers, he and Ittou Hagane are the most dedicated to Noroi, having almost completely given up their own emotions in his service. Ensai in particular has tried for many years to bring Noroi's plans to fruition, and finally bring the True Eternity where Noroi would subjugate humanity and bring a forced peace throughout the world.

As a leader, he is calm and collected, trying to take the most pragmatic course that would help Noroi, and willingly sacrificing his forces to improve their chances of success. One of the few times he showed any concern for anyone was when faced with Ittou Hagane's virtually certain sacrifice.

As the leader of the faction, Noroi has given him the power not only to summon genins, but also to bring back from the dead their more powerful allies, such as some of the Kainin, and even the Red Guardian Kikyou-Dayu.

History
(Spoilers ahead)

A long time ago, Ensai, then known as Ensai Utsuroi, was a fairly renowned painter, creating many amazing paintings that many would come to see. However, he made them for his own pleasure, refusing the many commissions he received for his work. This changed when the local lord used the lives of his family and friends as leverage, forcing Ensai to create paintings of the lord's choosing at a private estate.

Ensai spent months forcibly creating paintings. The lord, pleased, ensured that he and his family were well-provided for, even when a famine struck the region. However, the villagers became jealous of Ensai and his family for living comfortably while they starved, and torched his estate, killing his family in the process. Afterwards, a bitter Ensai spent all his time painting his dead family. This eventually angered the lord, who exiled Ensai after smashing his eyes to increase the value of his old work.

Ensai wandered the region, until seeing a red light despite his blindness. Thus Ensai encountered Noroi, then inhabiting the body of a weasel. Ensai was the first one able to hear Noroi since his arrival on Earth, thanks to their similar hatred of humanity. Noroi spoke of his hatred against humans and his plans to stop them from destroying the world, but was in a reduced state after losing a fight against the Crescent Moons. Overjoyed for the first time in years, Ensai professed his devotion to him, stabbing himself with his sword as proof of his loyalty, and created the Noroi Faction.

Over the years, Ensai and Noroi brought fear and terror to many, eventually increasing Noroi's power once more. Over the years, they created the Tetra Castles, who serve as focal points of Noroi's power, all defended by the Tetra Sealers, individuals like Ensai with great power through their hatred against humanity. However, their efforts were stymied by the Crescent Moons efforts. Eventually, Noroi proclaimed that too many in the current era would counter their efforts, but that there was a time in the future which would prove ideal for their plans to create the Eternal Night.

Current day
(Major Spoilers ahead)

This led to Orochimaru stealing the Time Bell on Ensai's orders, sending the Noroi Faction as well as Haruka and Subaru many years into the future, right into the current era where the game begins. As the time travel exhausted most of Noroi's power once more, Ensai sends Orochimaru and some minions to retrieve the current Dragonian, so that his power can revitalize Noroi. However, this fails when Haruka arrives and with the help of the current Crescent Moon ninjas repels their assault. Not only that, but the Crescent Moons had been preparing a powerful seal for Noroi's eventual return. This seal brought intense pain to all those gifted with Noroi's power, with the strongest among them being the most affected.

Consequently, Ensai and the rest of the Tetra Sealers retreat to the Castle Infinity, their main base hidden in a dimensional pocket, and Ensai decides to send the weaker kainins and genins to stop and slay the Crescent Moons, worried that they would only gain power as time passes. As the Seal progressively becomes weaker, he decides to send Orochimaru along with his casle, as the building's presence in the human world further degrades the seal's power and gathers power for Noroi. To replenish their ranks, he then revives the slain Kikyou-Dayu into a monstrous arm that he latches onto the captured Subaru, then sends the possessed Blade to slay their foes as well. As all those efforts prove fruitless, Ittou Hagane himself decides to smash the seal with his own hands, despite being much too powerful to be unaffected by the seal's power. Ensai is at first against this plan, as it would surely lead to Ittou's death, but is convined by his words that Noroi's life is forfeit if they do not act soon.

When Ittou Hagane is defeated, however, Ensai realises their situation has become virtually hopeless, and simply waits for the Blades eventual arrival. However, his hope is rekindled when a dispossessed Kikyou-Dayu whispers to him from beyond the grave, telling him how she cursed Subaru with her power. When the Blades reach his castle, he is defeated by their power, but tricks them by claiming they can find a weakened Noroi in Castle Infinity. Haruka and Narika dash inside while Nubaru guards Ensai, but Kikyou's curse takes hold and incapacitates her with euphoria.