Ao to Kuro no Kyoukaisen

Stellar Calendar 81st day of year 1993. Due to a large scale explosion the the manufacturing city Nowal, the world was covered by a black smoke screen. From then the amount of rainfall dropped rapidly. Due to this the people on this planet came to call it "The world where rain does not fall." Approximately one hundred years later—

There is a witch who stole the world's rain and labelled the "Rain Girl" as a result. Then, a single young man approached her as her fated partner. He was also known as the "Clear (weather) Boy." This story starts after the meeting between these two incompatible people.

(Source: DengekiBunko, translated)