I like this game a lot, but one thing I don't like is that if you don't do every one of the wandering battles (which seems reasonable in most RPGs) then you don't have enough levels to beat the bosses, and, moreover, the wandering battles before Sauna Sign become inaccessible after a point, making it impossible to get the required levels if you missed them. This feels very bad, so I think you should either:
* Make it required to fight every wandering battle before leaving any area
* Make the battles easier so you can still finish if you're low-level
I prefer the second option because I'm not really convinced there's much of a narrative purpose in having to do the wandering battles (especially since a lot of them are palette-swaps of each other) but, you understand this game better than me, so I think just avoiding combat softlocks is strictly required.