Suzuhara Nao, an expert observer of migratory birds, becomes a substitute teacher at an elementary school. She's in charge of of first-year students and doesn't have much passion for her job. One of her young students named Reina becomes attached to her new teacher. One day, Nao knows about bruises on Reina and realizes that she is the victim of child abuse. At first Nao doesn't say anything, but Nao notices more bruises with each passing day and Reina's absences from school become more frequent. Nao's maternal instincts kicks in and she decides to take care of Reina. Nao & Reina then takes a train from their native Hokkaido to Tokyo ...