Thanks for the answering my dumbass question. I appreciate the answer and the explanation. Have a good one.Because the game's engine has a limit to still add girls, Zell created 2 parts: Part A (where you start with no skills) and B (where you already unlocked all skills in the game). I shall say FOBS has no story/lore/whatever explains why you go hunting monster girls, so it doesn't matter if you play part B before part A, but I suggest to play A before B to stablish an order when playing FOBS.
Also, as I mentioned, some girls appear only in A and others only in B.
Edit.: This is explained in the first page of this threat