[Jan-Poo]

Spoiler for Episode5 epitaph:

It isn't a bad reasoning. After ep5 I also started taking in consideration the possibility that the river is a railway. This concept was already introduced by the "enoura theory", however the enoura theory has been completely denied by confirming that odawara is definitely not Kinzo's hometown. The problem I had with the railway theory is that it lacked any connection with the sea, but it looks like you have found a possible one.

The problem is that at this point if this is really the right direction, it is almost impossible for a non japanese to progress further. It is already difficult as it is to find a complete railway chart for us, certainly you cannot find it in your atlas. And if the riddle is even further based on kanji for the village and the shore it gets even more difficult.

I'd also need to better understand what Rosa said about the ten checkpoint travel. "ougon kyou" and "ougon no sato", seem to have some importance, but I can't really get this one.