Thanks, but I already know about the hidden stuff in the files. I found some of them by myself and some by reading on the internet. And if I remember correctly, the most interesting theory is that the long story from Yuri.chr file is the backstory of a character in the next game, the woman pic from Natsuki.chr is the character of that story, and I forgot about the rest.
Although it's unclear whether it's true, this is not your ordinary visual novel indeed..