Originally Posted by blueDC

From Kementerian Luar Negeri (Ministry of Foreign Affairs):

http://www.kln.gov.my/english/visain...ian/japan.html

You'll need a visa to clear immigration. Without one, you'll have to stay in the airport the whole time. Good news with the visa: it's free. Once you get a visa, 10 hours is more than enough time to visit Narita (or Tokyo). Immigration can be as quick as 5 minutes or as long as one hour (entering AND exiting the country) depending on time of day. I would return to the airport 2 hours before your flight just to be safe assuming your bags are checked through and you already have a boarding pass for your next flight.