Somewhere there exist an infinite dungeon, with endless hoards of monsters residing in it. Because of some magic, any adventurer entering it will start at level 1, and no one has managed to complete the dungeon.
An alchemist tried to deal with this issue, and created a Doll, the ultimate support partner.
As the apprentice of the alchemist, you shall bring along the Doll and discover the mysteries of the dungeon.