The story takes place in an underground dungeon mined out by slaves who where brought there by monsters from various places on earth.
You play as one of the female slaves who were captured by monsters during their raid on your village. Surrounded by many other female slaves in a cell you decide that your goal is to escape alone or help others to leave this place safely with you.
During your gameplay you will come across a few other slaves who also took an initiative to look for a way out. They will give you more information on your current situation and support you with their abilities.
However, if you decide to look further into what is happening and prevent the monsters from future enslaving more girls, you will be able to go further into the castle and stop its mastermind. On your way there you will be able to learn more about the history of the castle and the people who built it.