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

The rain never stops. And the people are beginning to be hunted by the Rain. Viscous, blue-colored entities. This sudden disaster is still beyond the control of national governments, leaving people to live in a state where terror and daily life coexist.

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

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

Twin brothers Sora and Umi, along with 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.