The world is infested with demons that are drawn to human desire, possessing people and objects to manifest physically and devour the souls of the innocent. To combat this threat, the student council executive committee of Sacred White Lily Academy secretly operates as a band of exorcists known as the Apostles. They are led by first-year high school student Renga Takayama, who serves as the executive committee president, and his younger sister Moegi Takayama, the Holy Mother who possesses the power to create sacred vessels called Holy Grails that are essential for sealing demons. Other early members include Suou Kagayama and Noshime Kinoshita.

During the academy's entrance ceremony in April, a demon appears on school grounds. As Renga and the others attempt to seal it with a Holy Grail, the vessel inexplicably shatters, leaving them in peril. Their salvation comes from a mysterious transfer student dressed as a priest, Chitose Amakusa. A pair of pitch‑black wings erupts from his back, and he instantly obliterates the demon. It is revealed that Chitose is possessed by the strongest of all demons, a being that destroys and devours other demons. Initially wary of Chitose’s nature, Renga gradually comes to trust him after seeing his sincere determination to protect people from demons. Chitose is accepted into the executive committee, and together they are drawn into a larger conflict against the Dukes, malevolent beings who plot to resurrect the King of the Demon World.

The Apostles’ primary duty is not only to exorcise demons but also to safeguard Moegi, for if a demon consumes the Holy Mother’s soul, it can open the Sin Place, the gate that connects the human world to the demon realm, allowing demons to cross freely. As the story progresses, Chitose’s past and the nature of the demon within him come into focus. A fragment of a Holy Grail called the Yohen Tenmoku is discovered inside a demon, prompting Renga and his team to travel to Kyoto to seek the former Apostle who crafted it, Inaba Togo, who initially refuses to cooperate. Meanwhile, Sinclair, a Duke who is also Chitose’s teacher and the creator of powerful demonic tools, reveals that he once wiped out the previous generation of Apostles. The higher authorities order the executive committee to suspend operations, but Renga defies them and ventures alone into hell to stop Sinclair and reclaim Chitose.

The first major story arc culminates in a desperate, all‑out battle against Sinclair and his forces. The Apostles fight at the risk of their own lives, leading to farewells among friends and the apparent conclusion of the first part. A second part, titled Holy Talker: The One Who Follows the Holy Spirit, begins immediately after, introducing new enemies who have released the Demon King’s soul and who target Chitose. However, the second part was halted after only three chapters, and the series remains on indefinite hiatus following the magazine’s cessation. The narrative thus covers the Apostles’ struggle to protect the Holy Mother, the mystery of Chitose’s dual nature, and the escalating war against the forces seeking to open the demon gate.