Riko is an energetic twelve year old orphan residing in the town of Oosu. She is very curious and tries to gain as much information she can on topics that the is interested in. She has been studying in order to become a cave raider. Having received her red whistle, she became an apprentice and is allowed to climb down into the upper levels of the Abyss. Her goal is to obtain the highest rank, the white whistle, and try to follow her Mother who disappeared inside the Abyss.