Originally Posted by
UAPremExecflyer
You need an onward boarding pass to access the transfer security line and the NH lounge. *A lounges, unless otherwise clearly specified, are departure lounges not arrivals.
No you don't, I have done this with just a copy of my itinerary (and once with nothing in writing). However, while there may well be a way to get back to arrivals, I sure don't know what it is, nor is it signed anywhere that I've been in Narita.
I would recommend against trying this.