Zouken Matou

Zouken Matou (間桐 臓硯) is Master of True Assassin in the Fifth Holy Grail War of Fate/stay night's Heaven's Feel scenario. He is the grandfather of Shinji Matou and Sakura Matou. He is the main antagonist of Heaven's Feel.

Background
Originally known as Makiri Zolgen (マキリ・ゾォルケン), he was the patriarch of the Zolgen family five hundred years before the Fifth Holy Grail War. They were a noble family that originated somewhere around Russia and were driven out of their homeland. The family later became known as Makiri when he changed his name to Zouken Makiri (マキリ臓硯). The family gained ties to both the Einzbern and Tohsaka families through his friendship with Justeaze Lizrich von Einzbern and Nagato Tohsaka, and he had enough of a relationship with Kishua Zelretch Schweinorg to be considered an a potential inheritor of the Jeweled Sword of Zelretch if not for Zelretch appraising the family as fundamentally evil.

Zouken had the dream of creating a utopia, having pursued it since he was around two hundred years old. He wanted to eliminate and cure all hatred and suffering. He felt grief upon finding that "paradise" did not exist in the world and its creation was impossible with a human body, and he instead wished to go to a place where it could be accomplished. Humanity has set limits, so he wished for it to go outside the spiral of the brain and the limits of the body to reach the infinity called the soul. Obtaining all creation and knowledge where no human can reach, it was not to make a new world, but to change his human life.

He sought the Holy Grail to be reborn and reach the ideal utopia, the unimaginable land. With a miracle beyond human reach, he sought to eliminate all of the evils of the world, risking his life for an ideal that could not be fulfilled. Though his enemies died, he kept seeking it despite knowing it was meaningless. He believed it was his reason to exist, all while hoping that his existence would bring about a successor. In order to overthrow his youthful anguish, he came up with that answer even if his life should not be compensated.

He was around three hundred years old as of the establishment of the Holy Grail War to fulfill his dream along with the Tohsaka and Einzbern families. He moved his family to Japan under the name Matou, and while it was to hide the family's identity, they needed something tying into their real name and used a play on words. Zouken proposed the system of "Master" and "Servant", while Nagato provided his property Fuyuki City and Justeaze developed the Heaven's Feel system, offered the homunculi vessels for the Grail, and became the core of the Great Grail. Justeaze utilized her own body to become the magic circuit of the Grail.

At the time, Zouken admired her deeply, and was devastated to see her sacrifice. He had decided to ensure that her sacrifice would not be in vain by keeping himself alive long enough to witness the moment the Grail becomes completed and reaches the gate. However, as the time went on, the frustration due to the incomplete Grail and the deterioration of his body over such long period had slowly caused him to forget his original intention, and had left him only the abnormal obsession about obtaining immortality.

Shrewd, powerful, and ancient, he is known as the grandfather of Shinji and Sakura and the father of Kariya and his brother Byakuya To conceal his status as the Matous' ancestor, he masquerades as a relative to his descendants, though some members of his family have long suspected he is much older than he appears given how Zouken's name has repeatedly appeared in the family tree. He has amassed a large and extensive library of sorcerous knowledge, yet his lessons are strict and harsh. Zouken considers Shinji to be a disgrace of a sorcerer, and believes Sakura may have more potential than her brother.

Because the Matou blood has thinned and no longer produces heirs naturally capable of sorcery, Shinji was incapable of becoming a true sorcerer so Zouken offered to adopt Tohsaka Sakura into the Matou when her father, Tokiomi, decided to train only his older daughter, Rin, to become his successor. Sakura was implanted with Zouken's magical worms to prepare her as a vessel for Angra Mainyu in the fifth Holy Grail War.

Personality
Zouken is a shrewd old man with plenty of knowledge on magecraft to the several centuries he has been alive. He is shown to be strict and harsh in the training of magi within his family and is becoming increasingly frustrated with the thinning bloodline of the Matou family preventing the birth of any natural-born magi.

Fate/Zero
In Fate/Zero, Zouken adopted Sakura Tohsaka into the Matou family approximately one year before the Fourth Holy Grail War after requesting Sakura's father Tokiomi for one of his daughters to become the heir to the Matou family. A few days after her adoption, Kariya Matou returns to Fuyuki City to visit his childhood friend Aoi Tohsaka and her two daughters and is horrified to learn that Aoi's younger daughter has been sent to the Matou family. Kariya, who had previously left the Matō family ten years prior to the 4th Holy Grail War out of disgust for his own family, confronts Zouken over the girl's adoption and learns that Sakura has already been subjected to the brutal training required to learn the Matou family's magecraft.

Disappointed with the lack of sorceric potential in Shinji and Byakuya, Shinji's father, Zouken blames Kariya for allowing the Matou's magical lineage decline since Kariya is the first in many generations to be naturally capable of sorcery. However, Kariya formulates a deal with Zouken where should Kariya obtain the Holy Grail, Zouken must allow Sakura to return to her family. Due to his lack of formal training, Kariya is implanted with the same magical worms as Sakura. However, Zouken does not truly expect Kariya to succeed, merely accepting Kariya's bargain on the whim that Kariya surpasses his expectations.

Normally he observes the Holy Grail War from a distance, but when Kirei Kotomine rescued Kariya and returned him to the Matou mansion. Zouken was intrigued by his action and later kept a close eye on him. Zouken used his worms to heal Kariya external injuries, Zouken admits to Kariya that he surpassed his expectation on survival and gifted him a Crest Worm as a fatherly gift. The crest worm gave Kariya more prana boost, he revealed that the crest worm was the same worm that claimed Sakura's virginity. As Kariya cries and becomes disgusted by his statement, Zouken enjoys his suffering.

Towards the end of the war, Zouken lurks in the shadows while observing Kariya successfully abducting Irisviel von Einzbern and handing her to Kirei. During this fateful meeting, Zouken reveals to Kotomine that he has enjoyed watching Kariya suffering and knows that Kariya's chance of winning is zero. When he goes on to comment to Kirei that they have the same scent, an aggravated Kotomine throws his black keys at him. Zouken disappears, remarking that they will meet again and he expects to witness Kirei's development.

At the end of the Fourth War, Zouken acquired the fragments of the destroyed Grail. He combined the fragments with his Crest worms, which he put inside Sakura's body. Though she was incomplete, this turned her into a second Lesser Grail.

Fate/stay night
Zouken only appears in the Heaven's Feel route, so his fate in the Fate route and Unlimited Blade Works route is unknown other than that he stayed with his original plan of non-participation without the incentive of Sakura awakening as the other Grail.

Heaven's Feel
Zouken is first encountered when Shiro walks Sakura back to her home and is greeted by Zouken.

After witnessing Rider lose to Saber, and enraged at Shinji's incompetence as a Master, Zouken summons True Assassin from the body of Assassin and becomes a Master in the 5th Holy Grail War. Using Sakura as a vessel for Angra Mainyu, the dark spirit that resides within the Holy Grail, he sets out with True Assassin to eliminate the other Masters and Servants.

Sakura soon gives into her dark side and Zouken loses control over her and his plans to acquire the Holy Grail. He is subsequently killed when Kirei Kotomine exorcises his body and Sakura destroys the remaining remnant of his heart.

However, Zouken's presence still remains. As the final battle for the Grail ensues, the last remaining worm of Zouken attempts to reach the Grail, before being interrupted by Illyasviel von Einzbern in her Dress of Heaven. This prompts the long-buried memory in Zouken, and why he has stayed alive for so long. Seeing Ilya in the Dress of Heaven, just like Justica 300 years ago, reminds him of everything, and Zouken finally accepts his end.

Fate/hollow ataraxia
In Fate/hollow ataraxia, Zouken is alive alongside Shinji and has a minor relevance. It is eventually revealed that Sakura assumed control of the Matou household, and both Zouken and Shinji are terrified of her.

Carnival Phantasm
Zouken has a minor role in Carnival Phantasm, only having appeared in two scenes (in which he tries to enter to the Ahnenerbe bathroom to no avail). He has been reduced to a gag character, and even Shinji mistreats him.

Abilities
He is a powerful magus who had altered his body through Familiar magecraft that he is now more of a monster than human. Zouken can eat normal food but for him it’s more efficient to directly leech life force for nourishment.

He cannot be killed by normal physical means because his body is made out of the worms. Fatal wounds can easily be shrugged off, and even if his body is destroyed, he can easily reform it by devouring a human. Then as long as his soul was intact, he could regenerate his former self.

Magecraft
He was the one that came up with the Command Spells for the Master and Servant in the Holy Grail system.

Blood Worms
Zouken uses methods somehow comparable to vampirism, and actually Shinji's ancestor from five centuries past. He has used a species of magical worms to sustain his long life. Blood Worms are the creatures that have come to make up the body of Matou Zouken in his attempt to prolong his life. His existence is essentially a conglomerate of Crest Worms with a special appetite for human flesh and blood that combine themselves to take a human form. Despite the blood-sucking habits, he is not considered to be an actual vampire that the Church would hunt. This human form allows him to interfere with the physical world as it binds his soul, on this plane of existence.

Worms
The lowest of all familiars. His personal Familiars are prana eating worms that can channel energy even when their host is no longer alive. Loves feasting on the energy of humans.

When the host is a male, they consume their bone marrow and part of the brain after shattering his spine, making him crippled in the process.

When it is a female, they absorb the mental energy created after sexual stimulation is made through the nervous system. Usually don't consume the flesh of women, but the uterus is their favorite meals. Will eat the placenta after giving its victim sexual pleasure strong enough to fry the nerves of the brain.

Shinji Matou's Book of False Attendant is made out of these.