Yukiya is a university student. One day, a girl called Eleonora suddenly appears in front of him and tells him that she will marry him. It seems she is princess and comes from a different world. According to her, she will need to have his baby to show her attractiveness. He doesn't know what to do, but she approaches him. However, Kotono, his old friend, takes part in it as well. Like this, baby making battle now starts....