Blue Exorcist season 4

The Knights of the True Cross begin holding discussions among the higher ranks to establish countermeasures to deal with the influx of low and mid-level demons caused by the Illuminati. Soon after this meeting, Rin and the other cram school students are informed by Mephisto that the Exorcism Certification Exams will be held sooner than originally planned due to the immediate demand for more Exorcists. To assist with this change, Arch Knight Lightning is appointed as a new instructor for the cram school. Lighting holds a big class that is eager to learn from him until he drives most of the students away by proclaiming they should become friends with the demons. After class, Lightning gets Rin and Ryuji to help clean his personal living quarters. During this, Ryuji begins struggling with the fact that he has lost sight of his reason for becoming an Exorcist and, inspired by Lightning's efficient summons and death verses, asks that he become his apprentice. Lightning initially declines this as he is unable to get the Kurikara in the process. However, after testing Ryuji in a death verse game, Lightning allows him to work as his assistant in order to pilfer his abilities.

Yukio starts investigating the true nature of the power that has started manifesting within his eyes. The situations in which this power appears all had one thing in common: they only appear when he is put in life-threatening situations. Yukio puts his own life on the line in a series of dangerous stunts in an attempt to awaken this hidden power. A day earlier, Rin, Konekomaru and Renzo begin studying for the Exorcism Certification Exams without Ryuji, who is out running errands for Lightning. Ryuji eventually meets up with the trio as he expresses his enthusiasm at being able to apprentice under Lightning. The next day, Rin and Shiemi go on a simple mission to exorcise coal tars appearing in an old house. They both end up trapped inside the house's basement, where they slightly express their feelings for each other before Rin busts them out of the basement by using his flames, much to the disarray of their supervising Exorcist, who instructed them not to destroy the building. Suddenly, Rin and Yukio receive a phone call from Mephisto. He informs the brothers that Shura has been missing for the past few days and orders them to locate her.

Mephisto deduces that Shura returned to her hometown of Towada in Aomori Prefecture. He instructs Rin and Yukio to go there and search for her. The brothers arrive in the snow-covered city near the Lake Towada area, where they stay lodging for the night. The next morning, Shura confronts Hachirotaro Okami, a powerful Hydra who claims territory at the lake and its surrounding areas. Initially summoning her because someone was snooping around his territory, Hachiro uses the opportunity to urge Shura to bear a child. When Shura refuses, Hachiro incapacitates her. Rin and Yukio arrive to find the unconscious Shura alone and injured. They bring her back to the lodging, where her injuries quickly heal. Shura awakens and explains to the brothers that her ancestor formed a blood oath with Hachiro where she was to bear a child before dying at age 30 to receive the demon's power. This lineage cycle would continue until it reached Shura herself. Contempt with breaking the cycle and dying in three years without bearing Hachiro a child, Shura tells the boys not to concern themselves with her before falling asleep. As the brothers go outside Shura's room to contact Mephisto, Hachiro kidnaps her.

Shura awakens outside to discover Hachiro right in front of her, who begins using his hypnotic powers to control her body. Rin and Yukio arrive to rescue Shura, but Hachiro pushes Rin back and uses his hypnosis to incapacitate Yukio. Hachiro plans to use Yukio and force Shura to conceive a child, but Rin uses his flames on the demon and breaks his control over them. Shura attempts to use her sword to commit suicide, but Hachiro stops her from doing so. Seeing as no party present wants Shura to perish, Yukio proposes to Hachiro that he will assure she conceives by any means necessary if the demon transfers her blood seal onto his own body. Hachiro initially refuses the offer, but agrees after Yukio shows his loyalty to him by seemingly incapacitating Rin with gunfire. As Hachiro begins transferring Shura's seal onto Yukio, he is suddenly ambushed from behind by Rin. As a result, Hachiro's humanoid vessel is destroyed by Rin's flames. Angered by Yukio's deception into undoing Shura's seal, Hachiro reveals his serpentine demon form and kidnaps her again. Renzo arrives to assist the Okumura brothers as Hachiro takes Shura into the icy deep waters of Lake Towada.

As Shura sinks into the lake with Hachiro, she remembers the days she spent with Shiro. Meanwhile, Rin, Yukio and Renzo act fast to save Shura, with Rin using his flames to burn open the multiple snake heads of the demon. Hachiro loses his grip on Shura during the assault and she attempts to escape, but the demon recaptures her. Hachiro resurfaces with Shura and confronts Rin and the others, regenerating his heads in the process. As Yukio and Renzo attempt to rescue Shura, Hachiro swats Renzo away and attempts to crush Yukio to death. Shura breaks free from the demon's grasp by using her sword, saving Yukio and declaring her independence from the demon as he gets scorched by Rin's flames. The repeated destruction and regeneration of Hachiro's demon form causes him to devolve into an ordinary snake in both body and mind. Shura asks the brothers to allow Hachiro to escape as reinforcements arrive by daybreak. Shura embraces the brothers for liberating her from Hachiro's blood oath as Renzo reunites with them after getting knocked out during the battle. Yukio collapses from his injuries and is brought back to a hospital at True Cross by Rin and Shura.

Mephisto reveals to Shura that the Illuminati managed to capture Hachiro. Shura threatens to harm Mephisto if he continues to meddle with the Okumura brothers. Later that night, Lightning begins his investigation into the Illuminati with Ryuji. Based on circumstantial evidence, Lightning speculates that the Japan branch of the True Cross Order is somehow directly tied to the Illuminati's founding and the Blue Night incident. The next morning, after receiving Rin's confession, Shiemi worries that she does not understand the difference between romantic love and friendship love. Unable to bear her confusion, Izumo suggests the two have a study sleepover and uses it as a guise to get Shiemi to read a shōjo manga series about romance. After reading it, Shiemi gets a better grasp at the concept of love. She rejects Rin the next morning at school, citing her inadequacy compared to others her age. Despite both having the intention of keeping their relationship as just being friends, Rin takes the rejection hard and is consoled by Konekomaru. During this, Ryuji receives a phone call from Lightning. After school, Lightning takes Ryuji with him to visit the Southern Cross Boys' Monastery, the church where the Okumura brothers were raised.