Hushed exchanges among the female student populace of Shinyo Academy center around an enigmatic supernatural entity. This entity is Boogiepop, a Shinigami who is rumored to murder people at the height of their beauty before their allure wanes. Few know of his true nature: a guardian who, between periods of dormancy, manifests as the alter ego of a high school girl named Touka Miyashita to fend off "the enemies of the world." Now, a string of mysterious disappearances—presumed by the school to be merely runaways—has caused Boogiepop to awaken. But somewhere in the academy, a menacing creature hides, waiting for its opportune moment to strike. Boogiepop wa Warawanai subtly explores the intrinsic associations between human beings and their perception of time, while delving into its characters' complex relationships, emotions, memories, and pasts. [Written by MAL Rewrite]

Unaired 13th episode of Boku wa Tomodachi ga Sukunai.

Growing out of the chaos of a global war, the city of Utopia is populated by humans and bioroids (artificial humans). On the surface, everything is harmonious, but tensions lurk. Into this seemingly perfect society comes a survivor of the wars, Deunan Knute, who carries a legacy that will turn out to be of critical importance to the future of humanity. 

(Source: ANN)

Ura Ex, extra short anime included in Blu-ray and the DVD releases of Ao no Exorcist.