Riiko Izawa has never had a boyfriend and she has been rejected by every boy she has ever had a crush on. When she returns a lost cell phone to an oddly dressed salesman, she mentions wanting a boyfriend so to thank her, he directs her to his company's website.When she visits the site, Riiko finds it's a site to create your own lover.Thinking its a game, she customizes and accidentally orders one. The next day, her new lover arrives. Following the instruction manual, she kisses him to wake him up and configure him to be in love with only her. She names him "Night." Three days later, she is shocked to learn that she only had him for a free trial. The salesman, Gaku Namikiri, tells her that she must now pay 100,000,000 yen for Night, however, they will waive the fee if she helps them to collect data about how women think and feel to help perfect future models.

Riiko must now keep Night's true nature of not being human a secret from everyone around her. She also soon finds herself in a love triangle between Night and her childhood friend Soshi, who declares his love for her out of fear he will lose her. As the series progresses, Night begins to develop real human emotions, enabling him to truly love Riiko but also resulting in system malfunctions. When Riiko almost loses Night due to the malfunctions, she realizes that he is the one she really loves. She apologizes to Soshi, who moves to Spain with his brother. As the series ends, Night begins to grow sleepier and sleepier. The problems developed by his exceeding his abilities eventually causes his machinery to stop working, resulting in his "death". Before he died, he wrote a letter directed to Soshi telling him what was happening and asking him to take care of Riiko. Gaku Namikiri then sent the letter to Soshi after giving Riiko some time to grieve, which brings Soshi back to Japan to be at her side again.