Several days have passed since the rain began. People have come to call the monsters that appeared with the rain "Rain."

The rain never stops. And people have begun to be attacked by the Rain. Blue, viscous entities. This sudden disaster is something nations still cannot handle, and people live their daily lives side-by-side with terror.

Amidst this, those with the power to oppose the Rain appeared. People began to call these ability users "Umbrellas." However, Umbrellas are consumed every time they defeat a Rain. As consumption progresses, they rampage and eventually turn into a Rain themselves.

The only way to stop an Umbrella's rampage is through skin-to-skin contact with those known as "Suns," who possess no combat power.

Twin brothers Sora and Umi, and Guest, are childhood friends. But on the day the rain started, Sora and Umi awakened as Umbrellas. When Guest realizes they are a Sun, the relationship between the three begins to change.