According to GaGaGa Bunko, an anime project of Tanaka Romeo's light novel "Jinrui wa Suitai Shimashita" was announced to get underway.

Jinrui wa Suitai Shimashita novel official website
PV of the novel (Youtube)

Synopsis:
It's been several centuries since human beings declined due to the steep drop in birthrates. The most prosperous species on the Earth are "Fairies", 10 cm tall creatures with high intelligence. I became a UN arbitrator between the humans and the fairies and returned to my hometown to help my grandfather. I thought my job would not be a tough one and visited one of the fairies' habitats to say hello to them but...

Source: GaGaGa Bunko

Update Nov 16th
According to GaGaGa Bunko, the anime will be aired in summer of 2012.

Source: Scan of the announcement