Magician Of The Depths

in a world in which, a long time ago, a mage was said to have been brought to destruction by a monster that ate it. without parents, kunimi and chisayo are picked up by the owner of the region and are made to work. one day chisayo receives a harsh punishment. kunimi who thought that it won’t be a good idea if this continues, takes his sister and runs away. but then, they are swallowed by a large sudden crack in the ground ?