Narita removed transit security for some flights coming from USA. I know UA and NH are part of that program, not sure SQ is part of it.
For this method: once you land, you have option to go upstairs (normal transit route/immigration) or enter transit area immediately (through the regular departure gate)
Note that there is transit security for everyone else (eg sq/nh flights from Singapore landing in Narita)
maybe a reason to pick nh/ua over sq... Or not
Last edited by paperwastage; Aug 11, 2019 at 1:35 pm