Tsuru no Ongaeshi (鶴の恩返し, lit. "Crane's Return of a Favor") is a story from Japanese folklore about a crane who returns a favor to a man. A variant of the story where a man marries the crane that returns the favor is known as Tsuru Nyōbō (鶴女房, "Crane Wife").
A man saves a crane that hunters had shot down. That night, a beautiful girl appears at the man's door and tells him she is his wife. The man tells her he is not wealthy enough to support them, but she tells him that she has a bag of rice that will fill their stomachs. Every day, the rice never goes down in the sack and always stays full.
The next day she tells the man that she is going into a room to make something and that he is not to come in until she is finished. Seven days have passed, and she finally comes out with a beautiful piece of clothing, but she is very skinny. She tells the man to go to the markets the following day and to sell this for a considerable price. He returns home and tells her he sold it for an excellent price. After that, they are now wealthy.
The wife then goes back into the room, telling him not to come in again until she is finished. The man's curiosity takes over, and he peeks in, realizing that the woman is the crane he saved. When the crane sees that the man has found her true identity, she says that she cannot stay there anymore and flies away, never returning.