Stockfish has just submitted some Achievement Flag Info for
OMORI Achievements:
You can view the flags they submitted here:
Flag submission by Stockfish for OMORIStockfish said:A lot of missable achievements because you can reach a certain point near the end of the game where it becomes impossible to go back and do most of these unless you have a save file to go back. Otherwise, you will have to start over from the beginning of the game. If there are any questions or concerns, do let me know. I'm still pretty new to submitting flags.