Just finished the game. …It was easier to go through the map files and find the passcodes for the “nani” and “naze” (actually nase) passwords, than it was to figure them out myself. There was no in-game close button at the title screen, and the English parts weren’t perfect. Hiding the save room was a bit annoying, but I discovered its existence through trawling the map files.
For future readers: The shortest way to get past the final boss is to go down until you see a ghost, go left and up to go upstairs, go to the upper-leftmost door in the upper-left corridor, examine the cutting board to pick up a knife, equip it from the menu (third option down), then open the fridge, get some apples, eat one to get to full health. Then exit that room, go up the middle path and use “2122” on the left code thing and “2114” on the right. Then go through the door, into the next room, and use the knife attack special skill twice to win. Worst end is getting no hiragana, neutral is getting some, true end is getting all.