Yoroshiku Master

One day when 17-year-old Sagara Kurumi accidently bumps into a guy on the streets, reins suddenly appear and binds 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's out as a light. But it does indeed seem like Kurumi's a santa and Kaito's her reindeer and that they've got an important job to do on Christmas Eve~

(Source: Dragon Voice Project)

Included one-shots:
Volume 1: Amai Kamiato
Volume 2: Eden no Tobira
Volume 3: Penguin Kakumei Side Story