The living, heavens, and underworld become connected after a Divine Gate is open, ushering an era of chaos where desires and conflict intersect. Only when the World Council was formed, peace and order is restored and the Divine Gate becomes an urban legend. In that world, boys and girls deemed fit by the World Council are gathered, who aim to reach the gate for their personal objectives. Those who reach the gate can remake the world even the past or future.
Source : wikipedia