Kyuutarou Horikita is the tall, dark and handsome… cleaning expert of Kurokado High. His classmates find him mysterious mostly because he's hard to get to know. One day in his club's room in the school's oldest building, he stumbles upon a sleeping maiden: transfer student Fumi Nishioka.

With nowhere else to go and having the eyes to see spiritual dirt, Fumi will learn from the cranky Kyuutaro how to rid the school of the grime that attracts spirit-damaging bugs, and how to fight the bugs themselves.

Has she finally found a place she can call home in the large house of Kyuutaro's small family of sweepers? Will her brazen goal of marrying a rich guy disgust or amuse them? And her heart, once it learns the way of purifying cleansing, will it be cleansed in return—in spite of her missing memories and her ever-looming secret?