Several thousand years ago, an inexplicable event known as the Cataclysm turned most of humanity into dust, sparing only a chosen few for reasons still unknown. Five thousand years after the collapse of civilization, over the last few decades, the remaining population has progressed from savage hunters to developing walled cities. However, in the year 902 of the new era calendar, mankind's efforts are unexpectedly cut short when mysterious black portals that spawn deadly monsters begin appearing out of nowhere.

Ryusui Itsuki, a 21st-century high school student and aspiring scientist, had led a peaceful life until the Cataclysm plunged him into an endless slumber. One day, awakened by a mysterious voice, he emerged from the abyss only to find himself in a world starkly different from his familiar surroundings. Dumbfounded by this new reality, Ryusui is determined to unravel the mystery of who turned mankind into dust and why. He embarks on a quest to rebuild the world using his scientific knowledge. However, his journey takes a chilling twist when he stumbles upon a mysterious black portal that brutally changes the trajectory of his life forever.

[Welcome Player Ryusui]