The mysterious cave system Abyss is the last unexplored area of the world. Whole generations of brave adventurers, known as cave divers, have dedicated themselves to its exploration, and many more will follow until all its mysteries are finally unraveled. The young girl Riko has dreamed since childhood of becoming a legendary cave diver like her mother and following her into the depths of the Abyss. During an exploration of the upper levels of the Abyss, she makes a discovery that will change her entire life. A dark fantasy epic like no other.