The main character is going to college this year. He is going to leave his parents' house and start living alone, which he has longed for! But then...

The contract he signed with his parents has been cancelled, and he has to move into an apartment he doesn't know. The place he moved to is where his three step sisters live. They are all complete messes in their personal lives and have been bothering him when they were at their parents' home.

He is forced to live with them and they expect to take of them just how he did back home. He does not want to and is trying to find another place to live. The sisters want to be taken care of, and will try to keep the virgin protagonist from leaving by doing naughty things to him.

Thus begins the struggle of the protagonist to take care of the useless sisters.

[From official site]