There are 34 direct and indirect flights connecting Hanoi and Tokyo every week, with the journey taking 9 hrs 45 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 one airports to choose from – but Tokyo Haneda International Airport (HND) 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 & Singapore Airlines.
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.