Let's see, in Kamidori different types of terrain require different amount of fatigue to cross, characters restore 1 fp per turn and 2 if they do nothing. There are also potions and special objects on maps to restore fatigue.
If you don't have enough fatigue, you cannot move, but still able to do anything else, like casting a spell or fighting.
I believe 5-10 fatigue per cell should be enough, maybe 20 in very rare cases. And 1-2 AP per cell.
On the other hand, we could use only AP to limit movement in most cases, and some types of terrain will increase fatigue, like swamp or thicket.
There are also skills and items that allow you, for example, move through the lava or fly. This way you cannot go everywhere in the very beginning of the game.