Itsuki is bad with people and even worse with girls. But he is entrusted with the missions to birth children with 12 maidens to save a dying world. Granpania is under attack, it needs a hero and star children desperately. So the King summons Itsuki and his childhood friend Mahiru to his world. To return home, Itsuki needs to fight monsters and get along with the ladies. The closer he is to the maidens prior to their union, the more power his prospective children have. To make matters even more complicated, Mahiro confesses to him that she is pregnant, but doesn't know who the father is, or whether there is a father at all. Is the child one of the Star Children? Or is he something else altogether?