Blue Exorcist, Volume 23 (Blue Exorcist #104-108)

The tragic story of what happened to Rin and Yukio's mother, Yuri Egin, continues to unfold. Yuri and Father Fujimoto were once up-and-coming young Exorcists involved in Section 13's extensive operation to research elixirs of immortality and develop clones to house the spirits of demons. The project seemed to be moving ahead until the unexpected manifestation of a demonic spirit into one of the clone bodies. And not just any demon - the most powerful demon of all: Satan!