You Are My Pet (2011)

On a rainy night, Eun-Yi walks home and finds a large blue box on front of her home. When she looks inside, she's shocked to see a man named In-Ho sitting in the box. Oddly enough, In-Ho reminds Eun-Yi of her former pet dog Momo. Eun-Yi then comes up with an arrangement. She will let In-Ho stay at her apartment if he will become her pet dog Momo.