My sister has wings hidden in her back In Gugyul-ri, a small seaside village, Nan-na(LEE Yo-sub) lives with his grandma but on the year he turns four, his world is interrupted by his sister Oh-gi(HAN Ye-rin) his grandma brings out of blue. Suddenly, Nan-na finds himself out of attention and is told to take care of his baby sister. Now Nan-na can't play with his friends and has to stay at home changing Oh-gi's diapers. To Nan-na, Oh-gi is just an intruder to his peaceful life. Because of dystrophy, Oh-gi gets her back hunched which makes Nan-na more ashamed of his sister. But when Nan-na and Oh-gi have to leave the seaside village and get separated, surprisingly Nan-na finds himself missing his sister and the feelings get stronger as day goes by.