Asiana Airlines provides a number of daily flights to Vietnam, mostly from Busan and Seoul. On the route from Korea to Hanoi (GMT+7), there are two daily flights. One departs at 21.05 (local time) from Busan and one from Seoul at 19.20. The lowest fare for these flights is approximately 580 USD for one way trip and 640USD for the round trip (15 day stay).
Asiana Airlines also operates daily flights to Ho Chi Minh City: One departs Busan at 21.20 (local time) and two others take off from Seoul at 19.10 and 8.40. The lowest price that is charged per ticket is 560USD for one way trip and 620USD for the round trip (15 day stay).