Thus far there's 3 state that I've found:
Normal
Corrupted
Hypnotized (it's kinda like corrupt +1)
Usually certain items/objects will turn you into one or another and certain things in the game require you to be in specific state to get (like barriers that require hypnotized state to get past)
Once you clear 3rd stage you can unlock the PC (only usable while normal) to check what CGs/Scenes you've unlocked (and some that might be just a teaser)
The picture while walking does change a bit more with whether you're under special effect like Aphrodisiac and such.
The site does hint at more things being possible.
It's not until the 5th stage that I see a BF-ish move (from succubus for now)
Well, I stopped playing after enjoying it a bit too much

will continue on it later.