Souren was a former Buddhist monk hailing from Tamil Buddhism who has lived for around 300 years. He witnessed endless death, and this gave him the twisted purpose of finding a reason for human death. He was excommunitcated by his master because he saw the origin of people.
He later entered the Mage's Association Clock Tower in London with Touko Aozaki and Cornelius Alba. Souren Araya attempted to reach Akasha by tracing the roots of the soul, something that is there but not there, in order to reach a group consciousness.
He is personally interested in the Demon Hunter Organization families, especially Shiki Ryougi.
He encounters Fujino Asagami, Kirie Fujou, and Lio Shirazumi, pressing them to awaken their innate abilities. He planned Fujino and Kirie to fight against Shiki in hopes that they would be able to defeat her, but also in part so the Counter Force would overlook his own operations.
Ogawa Apartment Complex
In his attempt to reach the Akasha, he perform an experiment on an apartment complex in Kayamihama, Mifune City. He used Touko's architecture blueprint to create the Ogawa Apartment. The Ogawa Apartment is the embodiment of Taikyokuzu (Ying and Yang); he placed the Taikyokuzu within a Taikyokuzu. Lio lived in the apartment for some time. The apartment walls has been inscribed with strange patterns which caused people to go into depression leading them to become insane thus driving them to their deaths.
He collaborated with Cornelius and in return; he will help kill Touko. Cornelius was responsible for the system at the Ogawa apartment, where only the brains of residents were kept alive and connected to puppet bodies. The experiment involved controlling the brain that was still functioning and implant their the thought processes into the replica puppets. There were 50 households in the apartment complex but only 30 of the household are real; the Enjou family were one of the subjects of the experiments. Araya created the Apartment Complex to create a cyclical loop in which the puppet residents repeat their last day before death as a means to discover an access to the Spiral of Origin. To avoid the Counter Force, he placed a powerful bounded field "Hounouden Rokujyuyonshou" so the experiment wouldn't leak out and the Counter Force wouldn't notice it.
Tomoe Enjou was able to escape from the repetitive spiral, something that Araya didn't expect. Before Tomoe left, Araya supposedly implanted an unconscious imprinting in this puppet to have an interest in Shiki. He plans to retrace the path of the Spiral of Origin by using Shiki's Mystic Eyes of Death Perception. To do so, Araya plans to transplant his brain into Shiki's body.
Souren is a tragic figure. Originally a wandering monk, his inability to save the lives of so many gave way to depression. His faith in humanity nearly crushed, he made his goal to locate the Spiral of Origin so that he may see the ultimate end of humanity and find meaning for so many deaths. His imposing appearance is often described in the novels. Touko herself commenting that he was "a man of hell". She describes him as a clumsy man but his confidence was stronger than anyone else's.
Whilst seemingly an insensitive man who is only concerned with using others towards his goal, his actions towards Fujino, Kirie, and Lio all seem to imply that he was acting out of genuine kindness and not just self-benefit.
Kara no Kyoukai
Araya is the main antagonist, although he is mentioned by other characters, he makes a full appearance in Paradox Spiral chapter.
Chapter 4: The Hollow Shrine
In June 1998, Touko overhears the nurses in the hospital that the previous counselor was Araya.
Chapter 3: Remaining Sense of Pain
Touko hands over Araya's sccess ticket to Shiki. Touko mentions that she originally made them for a friend to access the Broad Bridge.
Chapter 1: Overlooking the Scenery
Kirie reveals to Touko "the man" who gave her spiritual abilities.
Chapter 5: Paradox Spiral
In November 1998, Tomoe brings Shiki to his apartment where he supposedly killed his parents. However Shiki revealed the true nature of the apartment to Tomoe and revealed the real corpses of his family. While they were in Tomoe's real apartment, they were attacked by reanimated corpses.
Araya meets Shiki the second time when she kills all the reanimated corpses. Shiki had difficulties reading his death lines because of his Śarīra. Araya subdue Shiki by imprisoning her within a barrier isolated from space. He allowed Tomoe to escape because he knew it would be a matter of time for him to expire.
When Cornelius was knocked out by Touko, he intervened and faced Touko. Touko seemingly defeated Araya with her Projection Machine but Touko soon realized the Araya she defeated was a puppet. Touko was later incapacitated by the real Araya when he pulled out her heart from behind. However she did not die as Araya kept her in a frozen state: he decapitated her and stored her head in a jar. He didn't kill her because he knew that the next Touko would respawn when she dies. He destroyed Touko Projection machine by destroying her briefcase. He handed over Touko's head to Cornelius.
When Tomoe entered his workshop through the sewers and found his original brain, Araya reveals his true nature as a puppet. Araya claims that Tomoe's love for Shiki is merely fabricated and that he simply imprinted such a desire in Tomoe's mind. Araya taunts Tomoe to confront him where he'll be waiting at the 10th floor.
As Tomoe takes the elevator to confront Araya, he grabs Shiki's knife. Tomoe finds Araya standing before him. He confirms his determination to kill Araya for his sake and his parents' death, claiming that they weren't sinful enough to die in such a cruel way. He charges head-on but Araya uses his bounded field to stall him. Tomoe's limbs are slowly torn away as he manages to stab Araya in the chest. He is eventually killed by Araya's power, commanding Tomoe's body to cease existence.
Due to Tomoe leaving behind Shiki's katana, Kanesada Kuji, inside the Ogawa Apartment's elevator, Shiki is able to easily break free upon finally gaining consciousness, and confront and outmatch Araya in battle.
Souren, while considered an average magus at face value, is highly skilled in the creation of Bounded Fields. The origin that he has is "Stillness". He has a Śarīra, the sacred remains of devout Buddhist masters, embedded within his left arm. It belonged to an enlightened one who achieved "becoming extinguished, alive", so it has a resistance to the Mystic Eyes of Death Perception. The ability to kill it by slashing the lines of death would require Shiki to decipher "advanced lines of death" that are levels higher than the normal concept of death, so she is unable to view such vulnerable parts by looking upon it. They are still just bones in the physical sense, so they are susceptible to burning to ashes and the force of a large impact is able to destroy them even with their natural protection.
He personally carries Rokudou Kyoukai, a three layered bounded field that completely surrounds his person and hides his presence. All those who enter the perimeter of the outer field are completely frozen in place in accordance with his origin of "Stillness", and as it is mobile, something normally impossible to accomplish, he can freely use it as a weapon. It is constantly crumbling with the passage of time, and it takes a length of time for Souren to recreate it. He calls the names Fugu, Kongou, Dakatsu, Taiten, Chougyou and Ouken when he uses it.
He has also constructed Hounouden Rokujyuyonshou, a bounded field that completely surrounds his workshop, Ogawa Apartment. The original architect was Aozaki, and it is a shrine for the Taikyokuzu, the diagram of the supreme ultimate. The building can be called the embodiment of his internal world, very similar to the concept of a Reality Marble, which gives him complete control over its internal workings. He has the ability to teleport though walls, send projections of his mind to different locations, and it also allow for regeneration after he is sliced by Shiki.
The building is a red, round, and symmetrical ten story building with five rooms on each side. It is used for Souren's experiments to find the meaning of death by watching the lives of the 64 families that take residence there. All of the collected families have life issues, including the family of Tomoe Enjou, and he drove them to suicide and murder with designs on the walls and floors. Afterward, he removed their brains and created identical puppet bodies for them to control. He began using them to create a “miniature world that concludes in a day”, where he would have all of the puppets act out their daily lives, with each day concluding by having them kill each other. Souren, hoping for their deaths to deviate from the previous days, revived the bodies by morning, where they would simply restart with the memories of the final day of their lives. The puppets live on one side, and the other side, hidden by a rotating elevator, is used to store their original corpses. He manages to hide the massive experiment, which would normally cause suspicions from even the smallest irregularity and the trail of information in modern society, by making it out to be a normal apartment.