Narita at 5:00… that's cutting it pretty short! You'll have to leave around 2:30 or 3:00 just to be sure you're there on time. Luckily Nippori station is just a few stops away. (that is, if you're thinking of taking the Tobu Line Skyliner out there).
O.D. Box is at Okachimachi station, one over from Ueno, though still in the Ueno area. I think they open at 11:00, or maybe 10:00.
Too bad you don't have time to go out to Mitaka to Hiker's Depot, where my friend Tomoyoshi Tsuchiya, the owner of the store, and one of the pioneers of ultralight in Japan, works. Everything in the store is dedicated to UL, and they've recently expanded (still a small store, though.
O.D. Box has recently gotten in the first batch of 2014 new gear and clothes, so it ought to be interesting.
My school is off until April 7, so my Friday is free.
Rick, you should join us! Be great to see you again, too! Especially since we haven't had any chances to talk UL while with other hikers!