From the Abyss: Dawn of the Deep Soul

In a world where every corner has been explored, the only remaining secret is the large cave "Abyss." The huge, bottomless, vertical cave that does not know where it continues is inhabited by wonderful and strange creatures, and there are precious relics that cannot be made by modern humans. The mysterious figure of "Abyss" attracts people and drives them to adventure. In this way, adventurers who have challenged large caves many times have gradually gained the title of "cave explorers". Rico, an orphan living in the town "Os" built on the edge of Abyss, dreams of one day becoming a great digger like her mother and solving the mysteries of Abyss. One day, taking the opportunity of the discovery of her mother Lysa's white flute, Rico decided to dive into the depths of Abyss. The amnesiac robot Leg, picked up by Rico, also decided to go with him in order to find his own memory. Rico was poisoned by the bullet-piercing beast on the fourth floor of the deep world. The one who saved Rico was Nanaki, the "skeleton". Nanaki also became the companion of the two, and the adventure of the three headed towards the fifth layer of the deep world where Portordo was located. There, they met a girl named Pluska...