|“||There were terrible cries for the first three days, but by the fourth day, she was silent. Today, she was thrown at dawn in the worm storage to test how well she would last, but, ho ho, she endured it for half a day and is still breathing. What do you know, the Tōsaka material isn't defective.||„|
|~ Zouken Matou|
Zouken Matou is the main antagonist of Fate/stay night Heaven's Feel route, he is the grandfather of Shinji and Sakura Matou and a villain from the Fate series. He first appears in the Heaven's Feel route. Zouken is actually around two centuries old, having used parasitic worms to continually expand his lifespan. In Heaven's Feel, he summons True Assassin from the corpse of Assassin, thus becoming the seventh Master in the fifth Holy Grail War.
Zouken was originally known as Zolgen Makiri and is the patriarch of the Matou family. The family later changed later became known as Makiri when he changed his name to Zouken Makiri, and it changed again upon making it into the "Matou" family.
Alongside Nagato Tohsaka and Justeaze Lizrich von Einzbern, he was one of the creators of Fuyuki's Holy Grail system along with Kischur Zelretch Schweinorg guidance. Back then, the true purpose of the Holy Grail was to reach the Gate of All Things, the root of the universe. Zouken proposed the system of "Master" and "Servant" while Nagato provided his property Fuyuki and Justica developed the Heaven's Feel system, offering the homunculi vessels for the Grail and becoming the core of the Great Grail. Justica would sacrifice herself by transforming into the Grail's magic circuit.
At the time, Zouken admired Justica so deeply that he was devastated to see her sacrifice. He decided to ensure that her sacrifice would not be in vain by keeping himself alive long enough to see the moment the Grail is completed and reaches the heavens. However, as time went on, his frustration caused by the incomplete Grail and the deterioration of his body over such a long period of time slowly caused him to forget his original intention and left him only with an abnormal obsession with immortality.
Shrewd, powerful, and ancient, he is known today as Shinji and Sakura's grandfather and the uncle of Kariya and his brother Byakuya. He conceals his status as the Matous' ancestor by masquerading as a relative to his descendants, which some of his family members have long suspected given how repeatedly Zouken's name has appeared in the family tree. He expresses a large and extensive library of sorcerous knowledge, but his lessons are often strict and harsh. He believes Shinji to be a disgrace as a sorcerer and believes Sakura to have more potential than her brother.
Since the Matou blood has thinned and no longer has heirs naturally capable of sorcery, Shinji was incapable of being a true sorcerer so Zouken offered to adopt Sakura Tohsaka into the Matou family when her father, Tokiomi Tohsaka, decided to only train his older daughter, Rin Tohsaka, to become his successor.
Sakura was implanted with Zouken's magical worms in preparation for her usage as a vessel for Angra Mainyu during the fifth Holy Grail War.
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.
Towards the end of the war, Zouken lurks in the shadows while observing Kariya successfully abducting Irisviel von Einzbern and handing her to Kirei Kotomine. 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.
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.
As he was not present in the Fate or Unlimited Blade Works arcs, it is presumed that Zouken Matou survived the fifth Grail War in these scenarios because it did not appear that he participated in the war. However, it is also presumed that Kirei Kotomine might have found and killed Zouken in order to settle an old score or grudge he had against Zouken in the other arcs.
Unlimited blade works
An interesting point is a suspicion that Zouken would have been killed by Gilgamesh in the basement of the Matou manor. Shinji has a casual conversation with Gilgamesh, who off-handedly crushes one of Zouken's bugs under his heel. It can be assumed that Kotomine Kirei wanted to both troll Shinji and get revenge upon Zouken on principle, thus hitting two birds with one stone.
Zouken is first encountered when Shirou Emiya 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 in to her dark side and Zouken loses control over her and his plans to acquire the Holy Grail. He is subsequently killed when Kotomine Kirei 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 and dies peacefully.
Zouken is a powerful magus with extensive knowledge. He cannot be killed by normal or physical means because his body is made out of the worms he uses to prolong his life span. Fatal wounds can easily be shrugged off, and he can easily reform his body by devouring a human even if his body is destroyed.
He was the one that came up with the Command Spells for the Master and Servant in the Holy Grail system.
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.
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, they don't consume the flesh of women, but the uterus is their favorite meal. 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.