The manga follows the story of a girl named Riiko and her love life. She is not successful with boys and gets picked on often while she is at school. When she helps out a salesman, he sells her a robotic boyfriend named Night. Though their interactions are awkward at first, she soon begins to fall in love with him. Despite that Night is a robot, he actually develops the ability to fall in love with Riiko and the two become an adorable couple. He protects her everywhere she goes and even enrolls at her school to be with her. Meanwhile, Riiko's childhood friend also develops an interest in her, causing a love triangle.
Of course, all good things eventually come to an end in these types of stories, and there's an ending that is nearly heartbreaking. I won't explain what happens here because I'm not a fan of having great stories spoiled -- but needless to say, the ending is a tearjerker.