JR Tokyo Eki Shinkansen Minami
Good luck finding this store, one of three inside the JR Tokyo Station. After asking around, you'll discover that it is inside the ticket area. Eventually you'll figure out that you can enter with just a 130-yen ticket, but then you still have to find the store itself. You'll wander round and round, because you don't speak Japanese, but you won't see it, and eventually you'll ask a guard who will look at a map and inform you that the store--the WRONG store--is outside. You'll say "no, inside", and he'll repeat that it's outside. You'll walk off and keep looking, until you spot an information counter. Thankfully the attendant will speak English, and she'll direct you towards the Shinkansen South Transfer Gate, and tell you you need a ticket. Fortunately, the 130-yen ticket you already bought will get you past that gate as well, and finally you'll find the kiosk!!!
Funny thing is, if you had been able to read Japanese, and you had seen the store's full name on the Japanese site, JR Tokai Tokyo Eki Shinkansen Minami-Rachinai, you would have had a clue, because eki means station, minami means south, and rachinai mean something like 'within bounds'.