One day, 17-year-old Sagara Kurumi accidentally bumps into a guy on the street, and reins suddenly appear, binding them both! What is this?! Things get even more confusing when the boy, Kaito, clasps her hands and calls her his master! When Kaito transforms into a reindeer, it just becomes too much for poor Kurumi, who is out for a light stroll. But it does indeed seem like Kurumi is a Santa and Kaito is her reindeer, and that they have an important job to do on Christmas Eve~