Robot maker, "Kronos Heaven", finally develops "Night Tenjo", the perfect male humanoid programmed to be devoted and completely loyal to his lover. The company chooses temp worker Riiko Izawa to take part in a 5-day free trial. At first, Riiko only sees Night as a household appliance. But when she finds out how deep Night's devotion to herself is, Riiko finds herself falling in love with him.

Joining the "love triangle" is Soshi Asamoto, an executive of Riiko's company. Other characters surrounding Riiko are Gaku Namikiri, the sales representative of Kronos Heaven, and Fujiko Wakabayashi, a cafe owner who gives romance-related advices to Riiko.