Holy fucking shit,
7.4GB uncompressed????

279 BGM files, 705 sound effects - hold on... You've got the entire RTP shipped here? Just on the Pictures folder alone, there are several duplicates, mirrored images, reference images, placeholders, even some photoshop files. Dear lord, you might want to do some cleanup!
Anyway, the main culprit for the absurdly large size is that, much like several VNs, there is no layering, each different facial expression is an entirely separate file:
game_dev_ENG\img\pictures\wildcat_portrait_Full_nude has 340 full body images, the only thing changing between them being the eyes and the mouth.
This not something that can be fixed for this game, but if you ever do another, please do learn how to use layers for the images instead of keeping 1624 separate files, 1.84GB, just for the main character's many facial variations. When commissioning an artist, be sure to ask them to deliver each variation as a separate png and have all of them with a standardized size, like 200x100px for eyebrows and mouth.
5 separate bodies, 10 separate eyes, 10 separate eyebrows, 16 separate mouths, 1 blush effect, 1 angry effect, 2 different sweat effects. A hell lot easier on everyone's hard drives and also on yourself for whenever you have to update or fix anything.
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On the game proper, the pause menu has some
really fucked up logic going on. Open it, go to Factions, press X or ESC to go back. All fine. Press X or ESC again, and the menu reloads that main pause screen. Only on the 3rd press it actually closes. Not only that, if you go to Factions, back, then Overview, it doesn't actually open the overview, it just reloads the pause menu.
I was fucking around with it and the game finally crashed after some 5 or so "back from pause menu to the pause menu"