In the world where every corner has been explored, the only remaining mystery is the big cave "Abys". I don’t know where it continues, the bottomless huge vertical cave, inhabited by strange and strange creatures, and slumbering precious relics that cannot be made by today’s human beings. "Abys" is full of incredible gestures that attract people and drive them to adventure. In this way, the adventurers who have challenged the big cave many times have successively obtained the title of "cave explorer".
Rico, an orphan who lives in the town "Os" built on the edge of the abyss, dreams of one day becoming a great explorer like her mother and solving the mystery of the abyss. One day like this, while exploring the abyss, Rico picked up a robot with the appearance of a boy.?
