concerning the mouse girl with the flag:
Yes they are in the game. sorta, not as 3 of them, just one. the 3 might have been to illustrate their graphics states.
I'm thinking we need a guide. so far I can't find everything in shiro no yakata. I've explored almost every avenue. cumming on some monstergirls causes them to activate, or change their sex animation.
some things I have found;
Crawling lets you pass somethings
there are several enemies which are the sole focus of multiple rooms, jackolantern mask in example not sure if theres a secret associated with it.
some doors are not working yet, such as in the basement with the dino girl or whatever and at the end of the hall of the green flying girl with one eye that opens.
also the purple girl in the dark room is unpassable, she won't go for your double and is uneffected by everything else.
I've only found 1 enemy type that interacts with the sex symbol power when you are too horny.
It looks like there's only 1 item in your inventory, it's a light sometims it gets turned off, by selecting it and pressing A you can turn it on again. also there are tabs and such but I can't figure out how to select them.
looking at the game files, there are several images I have not found that I assume are hidden somewhere and lead to something. like the rope, I have yet to find the rope in the game. also at somepoint something make you lose your lamp on restart so you walk slow in dark rooms. not sure what thats about. it doesn't hide you in dark rooms, it just makes you not be abe to see clearly.
some pngs are unopennable on my machine, probably some newer unnecessary png format to prevent people from viewing it without a special codex or library.