I toughed it out through the bugs and incompleteness, found the weight gain content. After going through the Seaside Cave south of the mountain the bandit quest is on, advancing onward to beat a boss to return to the starter town, checking a new room in the hero hall and going to a snow place, and beating another boss with no explanation, you get to an overworld map. There’s a town in between two caves; go there. Party will split up to shop, and you can go into the leftmost building to buy food. Don’t know if you need to complete the surprise horror segment in the third building from the left first, I just stumbled into that, but doing it reunites the party. Sadly, only Hannah and Celina can gain. Buying food is the only way to gain weight unfortunately, unless someone wants to do a bug fix; the next portion, going through the second cave and entering a temple, softlocks you due to the only exit to the temple depositing you below it on the overworld, in an area where your only option is to return to the temple. At least it teases at weight skills being unlocked and being able to eat slimes, and there’s files for more characters who might join the party who can gain, but this one bug just halts all progress.
EDIT: Found the overworld map! It’s Map200! But since I have no idea what I’m doing, I don’t think I can fix it properly.