In the specific case of Vietnam, all it's people think that they came from dragons and fairies, all create many stories around that topic and how they fall of the heaven and start the kings line. They also have a lot of myths about the creation of the world, some animals like why duck sleeps in one leg, and some exotic fruits like watermelon. Many of this involve impossible love stories that show big hearts and teach many values.
In the other hand, they have a lots of urban legends around war, spies, heroes and treason. Almost all of this stories doesn't have any historical support and many of them has been confirmed as lies, but vietnamese still believing on them and will hardly quit to such stories.
Taking into account that they are a very traditional and reserved culture, you can imagine the tone of all thier myths and urban legends... they are beautiful, full of good messages, color and creativity.
http://www.marymount.k12.ny.us/marynet/StudentResources/art/southeastasia/vietnam/html/vietmyths.html, pictures taken from the same page.