The Abyss is a vast chasm plunging deep into the earth, teeming with enigmatic creatures and artifacts from an era long gone. How did it form? What awaits at its base? Countless courageous souls, called Divers, have attempted to unravel these mysteries by fearlessly descending into its darkest depths. The elite among them, the White Whistles, are revered as legends by those who stay on the surface. Riko, the daughter of the vanished White Whistle Lyza the Annihilator, dreams of following in her mother’s footsteps and exploring the Abyss’s deepest reaches. Yet, as a novice Red Whistle, she is restricted to its uppermost layer. Despite this, Riko stumbles upon a mysterious robot that looks like an ordinary young boy. She names him Reg, and he has no memory of what happened before he was found. Convinced that the technology behind Reg must originate from the Abyss’s depths, the pair resolve to descend into the chasm to recover his memories and witness the bottom of the great pit firsthand. However, they remain unaware of the harsh reality that defines the true nature of the Abyss.