Alright, an update on what I will call "Apostle: Rebellion - The Mystery of Translucence". Just raised this issue in the Kagura games discord, and one of the staff said that they'll bring it up. This way, we'll know if it's truly a bug, or just not implemented.
On my end, I've installed debugging, and I'll try to actively debug the game to see what files are being called, and what parameters they have. For this, could someone from here upload a save of just before when one of the main heroines are naked (or almost naked)? For example, Miyabi's first event has her top removed. Could someone upload a save just before that event? Any other scenes which have a nude character would be good.
For those techy guys out there, I want to do that because when a picture is displayed, it will call a function to display that image and take that image from a file. Since this one is a nude one, this means that either a different file was called in said scene as opposed to say, the beginning scenes where they are all clothed.