Mulan

The country is at war and the emperor has declared that one man from every family has to serve in the Imperial army. Since Mulan is the only child in the family and a woman, the only plans that her family have for her are for her to be married off. This also means that her father must serve in the army even though he is now old and decrepit. To save her father, Mulan cuts her hair and dresses as a man so that she can take his place as his son.