The planet Izumo gave rise to humans, who named the planet they lived on "Izumo" and its sister planet in the sky "Takamagahara." One day, a faction called the "Yaoyorozu no kami" or the "Yaoyorozu no Magakami" descended onto Izumo with the only goal of killing the humans. For their survival, they splintered 70,035 blades and forged them into 12 Sentinels. From then on, Izumo started its long and arduous crusade, exchanging inordinate lives lost for the fall of one Kami after another, shattering countless mortal blades to forge the twelve Sentinels.

In the merciless fight for survival, Izumo used the might of the Edict Edges to light up their uncivilized world of darkness in less than ten Amber Eras, building cities of dazzling neon lights. However, it wasn't enough to defeat the Kami. In continuing to resist the Kamigami, humanity eventually became Oni. No matter what they tried, their battle was meaningless. Izumo and Takamagahara had slowly started to sink into the Shadow of IX and the planets were destroyed. In the modern day, their history is erased. Academics hold various views regarding its disappearance, but none can solve the mystery.

At present time, as a member of the Nameless and a guest in Penacony, Planet of Festivities, you stay at the Reverie Hotel before going into the Dreamscapes. In the hotel, you've met a peculiar, mysterious woman, carrying a large sword reminiscent of an odachi, who has before asked you for directions, despite the hotel not being that hard to navigate. Acheron is a tall woman claiming to be a Galaxy Ranger with pale skin, long dark purple hair that covers the left side of her face, and bright violet eyes with pink highlights and diamond shaped pupils. Only when her sword is unsheath that her hazy memories start to become clearer. This time, however, she entered your room's open door, forgetting where her room was.

— ...Have I come to the wrong room? This can't be. Before I said anything, I even made sure that I had the right room number...