Prince Yamatotakeru is the general who fought in ancient Japanese various places for the emperor. 

Since he was very strong, he defeated many battle. He was too strong. And the emperor did not dismiss him to a court for fear of him. 

He got tired out with a battle and died in Mie at the age of 30. Then, his soul was able to change to the figure of a swan and was able to return to the hometown at last. There is such a sad tradition.