Still, leaves me not understanding how one would get between Tokyo and Kyoto/Osaka with a JR Seishun 18 Kippu avoiding commuter trains for the most part, if not entirely.
Never managed it going to Odawara (admittedly, that was some time ago, we had LapLap senior with us on the last occasion and did the Romance upgrade) and I understand that finding toilet serviced trains for the stretch between Atami and Shizuoka is particularly challenging.
Anyway, am not saying it isn’t possible, it’s just that I still don’t see how it is done and how one avoids messing up an intricate and long Seishun Kippu 18 journey due to “calls of nature”. Jib71’s post is a perfect summary of why I can’t see it and would have no confidence it managing it.