Humanity Has Declined

Humanity Has Declined, or Jinrui Wa Suitai Shimashita, is a post-apocalyptic, fantasy story written by Romeo Tanaka and first published in light novel format in May of 2007. 11 volumes were released as part of the story and the franchise was adapted into three different manga and an anime series.

Setting
Humanity Has Declined is set in a post-apocalyptic world wherein humanity has fallen into decline. What remains are ruins of the large civilization that once was, whereas the actual people live in villages and other, small communities. As humanity has returned to a simpler life with less luxuries, a new race has appeared and overtaken it in terms of development. These are the fairies, who are small, eccentric creatures that are highly intelligent despite their quirky nature.

The story largely takes place in and around a rural village that has limited access to electricity and endures all manner of difficulties.

The Fairies
The Mediator often refers to Fairies as "The New Humanity" as they are more plentiful and thriving than the actual humans. They are small creatures with large heads that always display a large smile regardless of how they feel. The fairies have squeaky voices and are very playful. In The Fairies' Subculture, it's revealed that fairies are easily influenced by hypes and, in general, attracted to fun. This leads to them using their mastery of technology to create strange and mostly useless inventions. When pushed, however, fairies can create something like a tool out of nothing but a tree in a manner of minutes.

Fairies are not only attracted to fun, they also live mostly on sweets. This is a problem because, despite their technological superiority, they can't actually make any. This is why they are fond of The Mediator and refer to her as Ms. Sweets. While most fairies are jovial in nature, the story does show that some can be mean-spirited and they can suffer from depression.

Light Novel
The light novel series ran from May 2007 to September 2016 and has 11 novels published. The novels were written by Romeo Tanaka with illustrations by Toru Yamasaki Sunaho Tobe. The first 4 novels were published in a short span between 2007 and 2008, but releases slowed down to about a single novel per year, with gaps as large as 14 months between some releases. The novels were not translated for an English release.

Manga
Four manga adaptations of the story were made. The first attempt, illustrated by Rei Neyuki, was put on hiatus after its first release and was eventually canceled. Terae Kichijo and Takuya Mitomi both illustrated different versions of the story, with Terae's version having 3 volumes out as of 2013 and Takuya's version having only 1. Neither of these versions was translated for an English release. A 4-panel manga, also by Takuya Mitomi, started serialization in August of 2012.

Anime
An anime adaptation directed by Seiji Kishi and written by Makoto Uezu aired in 2012 and received 12 episodes, which cover 7 of the story's arcs. 6 bonus episodes were created, called Mankind's Survival of the Fittest. Animation was handled by AIC A.S.T.A. and the show has been released outside of Japan as a subs-only DVD and Blu-Ray release.

Chronology
The anime airs the story arcs in the following order: The key events of the story are The Mediator finishing school, her first job, her meeting The Assistant, and her sabotaging the Human Monument Project. Because of that, the actual chronological order of events is as follows: Since the story is paced around the broadcasting order, it isn't worthwhile to watch the episodes chronologically. Mankind's Survival of the Fittest has no set place in the timeline, but likely fits between The Fairy's Earth and The Fairy's Survival Skills. However, it's likely not to be canonical at all.
 * 1) The Fairy's Secret Factory
 * 2) The Fairies' Subculture
 * 3) The Fairies' Homecoming
 * 4) The Fairies' Time Management
 * 5) The Fairy's Survival Skills
 * 6) The Fairy's Earth
 * 7) The Fairy's Secret Tea Party
 * 8) Mankind's Survival of the Fittest
 * 1) The Fairy's Secret Tea Party (The Mediator is a young girl attending school)
 * 2) The Fairy's Earth (The Mediator takes on her first job)
 * 3) The Fairy's Time Management (The Assistant is introduced)
 * 4) The Fairy's Survival Skills
 * 5) The Fairies' Subculture (Silver appears to partake in The Human Monument Project and then abandons it)
 * 6) The Fairies' Homecoming (The Human Monument Project continues with The Director and is sabotaged by the protagonist)
 * 7) The Fairy's Secret Factory