I am travelling from Mumbai to San Fran via Narita Airport. Do I need transit visa? If yes can I get visa on arrival?
Narita airport transit visa requirement
Do you intend to leave the secure part of the airport?
As karazyal says, it comes down to whether you need to leave the secure (airside) part of the airport.
Here is what the Narita airport website says on the matter
Aircraft can only operate between 6:00AM and 12:00AM at Narita Airport.
Passengers cannot remain in the passenger terminals on the airside (before arrival procedures and after departure procedures) outside of those times.
Passengers transiting overnight must complete arrival immigration and customs procedures. However, some passengers may need a visa at that time.
If you are in doubt concerning this, please contact your airline of the Immigration office directly in advance.
So the answer really is.. it depends. If you have an overnight stop in Narita you may need a visa. Whether you need a visa also depends on what passport you are travelling. If you are travelling with a US passport I think you won't need one, if you are travelling with an Indian one, then you probably will
Probably best to check with your airline as advised by the Narita airport site.