A Gray Rain is Going to Fall(鈍色ノ雨ガ降ッテクルッ)

Is this Japan in the near future or a place that closely resembles Japan? In a town where the weather forecast always ends with an announcement about a 'dull rain', people live their lives constantly worrying about the rain. The 'dull rain' is said to be the vapour that forms when a substance called H.U.A.N. in the air combines with another substance called Violence (VIOLENCE), which rises into the sky and forms clouds. However, neither clouds nor rain is visible to the human eye, nor do we know what happens when they fall.