There are 81 direct and indirect flights connecting Hanoi and Tokyo every week, with the journey taking 11 hrs 40 mins on average.
Or, if you're fairly flexible on dates, try to get a last minute-deal by regularly checking the Netflights website.
Tokyo actually has two airports to choose from – but New Tokyo International Airport (NRT) is the usually the cheapest option. If you need to fly into a specific airport, adjust your search to focus on those flights. The most popular airlines include Cathay Pacific, China Southern Airlines & Korean Air.
But if you can't find one which is right for you, try looking at flights to other cities in Japan to check out some other options.