Several days have passed since the rain began to fall. Monsters that appeared with the rain came to be known as "Rain."

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

Amidst this, those with the power to oppose the Rain appeared. People began to call these ability users "Umbrellas." However, Umbrellas are drained every time they defeat a Rain. As they deplete, they lose control, eventually turning into a Rain themselves.

The only way to stop an Umbrella's loss of control is through skin-to-skin contact with those called "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.