Luna-tan: 1-mannen no Himitsu

There was a land that kept the prosperity of the world using the energy Mana of the titans called Luna. However, when a tsunami struck the world, the land was destroyed. The story takes place ten thousand years after the huge tsunami in the underground. Mokugyo and Toriiruka are the main characters, who are strange animals. "Why are we here?" "I thought we were in somewhere peaceful..." What exactly happened ten thousand years ago? Can Mokugyou and Toriiruka safely return to the surface?