Originally Posted by
Often1
It is unlikely that NH will treat the transfer between two tickets at NRT as a transit. This leaves OP "stranded" at MEX and purchasing a new ticket back to the US.
I think that MEX-NRT-EWR is a very odd routing. I think that there is a risk that the airline will think that NRT is the intended destination and that the passenger is trying to abuse the system by showing up at NRT passport control and no-showing from the NRT-EWR leg. The airline might therefore deny boarding at MEX.