4 Angels and 4 Devils are sent to Earth, where they learn everything they need to become Guardian Angels and Guardian Devils. The Angels and Devils are required to form pairs as part of their education, each of which will have to deal with a human being, known as Earthly Ones, and help them choose between the right and wrong way in life without being discovered. Angels and Devils cannot operate at the same time, so they decide, clashing in the Challenge Room, who will work first. Moreover, they are subject to the V.E.T.O.