Yuzu, a girl living an idyllic life in an enclosed paradise, could not stop questioning about what might lie outside. One day, a boy named Taro invades that paradise and disrupts its peace. It turns out that the world Yuzu lives in is an experiment run by a scientist from the technopolis of Zelas. Yuzu finds herself outside, in Zelas, on Earth in the year 2155. The culture of the technopolis has lost all fear of god and is openly conducting human experiments. Yuzu, Taro, and others must find their way to a place of safety, and thus they decide to head into space.

December 20th, 198X. Mysteriously, people across the globe witness the same dark dream. Soon after, the number of humans unable to wake from their sleep begins to increase steadily. There are reports of life-like "R-dreams" that are experienced collectively and haunted with "Zel" - nightmare creatures. Hokuto, a struggling art student, is doubtful of R-dreams until he falls into one. There, he meets new friends, battles with the Zel, and tries to understand the nature of this dangerous phenomenon. Related Series Deep Green (Sequel) Ryuon (Side Story)