Chiaki Haruse, the owner of the struggling used bookstore "Kotatsudou," was on the verge of closing down, filled with despair.

Appearing before him then was Ren Shinohara, a mysterious beautiful girl. Ren offered to help rebuild the used bookstore, but in return, she demanded "marriage" from Chiaki.

Pressed by Ren, who claimed she needed to understand the bonds of family, Chiaki, though bewildered, accepted the contract marriage.

Thus began a slightly strange newlywed life with Ren, who aimed for "the perfect family."

Though perplexed by Ren, who was out of touch with common sense, Chiaki gradually began to be drawn to her.