Twelve young people living in modern-day Tokyo are caught in a sudden, deadly explosion, only to awaken with their souls bound to a mysterious fantasy world called Protolexa. Cast onto this strange planet on "the other side of the sky," the group discovers they have been drawn into a struggle far greater than themselves. Together they must survive, uncover the truth behind their deaths and their new existence, and find a way through the perils of Protolexa, with the bonds they form along the way shaping their fate.