I got stuck a bit there too, but after some event in town, one of the 抜闘士 talks about a new path opening up, and then if you teleport back to B13, a rock is in the sand you can jump over, just to the left of the teleport pad. https://dl.dropbox.com/s/kin4ih2o9hhw5aw/Untitled-1.png
For some...