Major bug: In the room with the green-haired boy before the underwater passage, there is no transfer back to the previous room. If you re-enter here after the Sister/Stein bosses, you're stuck.
That aside, I'm really enjoying this. The humour is great, the game is very well-balanced, there is an interesting variety of skills and strategies, and a definite gradual increase in actual difficulty (not just in stats). Kazuki and Minori are adorable
There are tons of spelling mistakes (the most amusing of which was Suphis playing a
hymen on the organ). I'd be happy to proofread the game for you, if you like. Also, some of the info such as character bios is too long for the screen.
In the Japan-themed world, it's odd that Ilva doesn't have a Japanese name. Is there a backstory reason that will become clear later?
In the first world, you can't walk behind the village elder's chair. The top half of the chair should be set to Star passability.
One of the robot enemies (I think it was 802, the one that inflicts Silence) has oddly low HP. Even Minori could one-shot him with a physical attack.
Stein could also do with more HP. It's set up to be an epic fight and it's over too quickly. On the whole, though, the level of challenge is just about right throughout. Several times I lost a character or two (there isn't much point in reviving during battle in this game, they just get killed again

) and managed a win with whoever I had left. The best one was versus Ichiyou, when I was down to just Minori and he still had about 1000 HP left. I just scraped a win there
Looking forward to the remaining chapters!