, or for short, is a Japanese light novel series written by Romeo Tanaka. The novels originally featured illustrations by TÃ Âru Yamasaki for the first six volumes, but Yamasaki was replaced by Sunaho Tobe in 2011. Shogakukan published 11 volumes from May 2007 to September 2016. Three manga adaptations have been produced. An anime adaptation produced by AIC A.S.T.A., directed by Seiji Kishi, and written by Makoto Uezu aired in Japan between July and September 2012. Sentai Filmworks has licensed the anime in North America.
Humanity Has Declined is set in a post-apocalyptic world where the human civilization has regressed and humanity keeps decreasing in numbers. The story follows an unnamed girl who acts as a mediator between humanity and the "fairies" who are small elf-like creatures attracted by sweets and happy things, but also have the habit to cause trouble to her with their powers in their endless search for amusement.
Humanity Has Declined began as a light novel series written by Romeo Tanaka. Shogakukan published 11 volumes between May 24, 2007, and September 16, 2016 under their Gagaga Bunko imprint; nine comprise the main story, while the other two are short story collections. For the first six volumes, the novels featured illustrations by TÃ Âru Yamasaki, but he was replaced by Sunaho Tobe in 2011. Shogakukan republished the novels with Tobe's illustrations between November 18, 2011, and March 16, 2012.
One chapter of a manga adaptation, illustrated by Rei Neyuki, was published in Shogakukan's Monthly Ikki magazine on January 25, 2010; however, the manga went on an indefinite hiatus and was ultimately cancelled. Another manga, illustrated by Takuya Mitomi, titled , was serialized in the same magazine from November 25, 2011, to May 25, 2012. Its chapters were collected in a single volume, released on July 30, 2012.
Mitomi also illustrated the four-panel comic strip manga , was serialized in Monthly Ikki from June 25 to August 25, 2012. A manga illustrated by Terae Kichijà  and titled was serialized in Media Factory's Monthly Comic Alive between January 27, 2012, and January 27, 2013. Three compiled volumes have been released.
An anime television series adaptation produced by AIC A.S.T.A. and directed by Seiji Kishi aired in Japan between July 2 and September 17, 2012; it was also simulcast by Crunchyroll. The screenplay was written by Makoto Uezu, and the chief animation director Kyà «ta Sakai based the character design used in the anime on Sunaho Tobe's original concepts. Six bonus episodes were included on the Blu-ray Disc and DVD releases. The opening theme is by Nano Ripe and the ending theme is by Masumi Ità Â. Sentai Filmworks has licensed the series for subtitled BD/DVD release in North America in December 2013.