You are at Endless Dungeon and aim to reach the deepest floor, but actually this is just a world with infinite floors that hasn't the end. You can meet survivor on the floor with tens numbers like 10, 20 and so on if there is a town there. Sometimes you will meet a cat girl named Leona and it seems that you always meet her even though this girl will try to stay away from you unless you can make her feel comfortable & safe with you. You just need to survive and stay alive to get out of there