Because of the constantly declining birth rates over many decades, human civilization is all but extinct. With only a few humans remaining, they survive in this post-apocalyptic world with what was left behind by the previous generations. Earth is now dominated by fairies, tiny creatures with extremely advanced technology, an obsession with candy, and a complete disregard for human safety. A young girl who has just finished her studies returns to her hometown and is designated as an official United Nations arbitrator. Her duty is to serve as a link between mankind and fairies, reassuring each side that both races can live together peacefully. She imagines this task will be easy enough, but controlling the disasters created by the oblivious fairies in their pursuit of candy will require a lot more effort than she initially believes.

More crazy antics abound as Nozomu Itoshiki (a.k.a Zetsubou-sensei), who is the worlds most negative person, tries to teach class 2-F about how life is filled with despair and darkness. A harder task than it first may seem, with his students being far from ordinary themselves, including the likes of the most positive girl he has ever met, his very own stalker, a foreign exchange student with split personalities and a perfectionist acting class president, due to the fact the real class president can't be seen by anyone, among others. (Source: ANN)

Ritsuka Tachibana has always been a good student, so she is completely shocked when she is suddenly summoned by the student council for breaking school rules. Led by Rem Kaginuki, the student council—also consisting of Urie Sogami, Shiki Natsumezaka, and Mage Nanashiro—tries to interrogate her, but it soon becomes clear that they have ulterior motives. However, this is only the beginning of Ritsuka's misfortune. When her mother gets kidnapped, her life is turned upside down, and Ritsuka gets drawn into a battle for supremacy between vampires and devils. Both groups are searching for the Grimoire, a forbidden item that allows its owner to rule the world, and Ritsuka is somehow connected to this strange artifact. The return of Ritsuka's protective brother Lindo from overseas gives her hope that life could return to normal. But even her sibling is harboring his own dark secrets. Ritsuka begins to question whom she can trust, and if she can ignore her growing attraction toward the devilishly handsome student council members.

Taito has been really sleepy lately, and keeps dreaming of a female vampire who says she has given him her poison. Sometimes he even thinks he hears her voice when he's awake. But after surviving an accident that should have killed him, Taito's world changes drastically and he realizes that his dreams are more real than he thought.