Hundreds of years from now, the last surviving humans discover the means of sending consciousness back through time, directly into people in the 21st century. These "travelers" assume the lives of seemingly random people, while secretly working as teams to perform missions in order to save humanity from a terrible future.

i is a Dimensional Police officer who jumps into "Retro World" (レトロワールド, Retoro Wārudo) to hunt down the criminal molikan.com organization "Doubt" (ダウト, Dauto). There, she faces off against her former partner Yui, who now works for Doubt.