So Succubi are not immune. Your character is completely immune however. A "gift" from the goddess.
As for corrupted enemy, there are a few, but I haven't done a good enough job explaining how exactly they're corrupted. That's something that's been on my mind. There are basically 2 sources for creatures. Some have been changed into monsters (Squiks, Alraune, bone centipede), and some come from the Demon world (goblins, ogre's)
Due to the direction of my story, I've been considering where I need to make alterations to make this flow better. Either by introducing more corrupted monsters, or by changing a bit of the back story.
Also there's one more thing but spoiler
So your character will not be physically transformed due to corruption... Or at least I don't have any current plans for that. However there is a corruption stat, which so far the game has only collected data for based on your game actions for future scenarios. In the update I'm planning to release on 08/03 (for patrons, 09/03 for free) I do have some text and dialogue changes based on your current corruption stat. Nothing major, but unless you guys are really MONSTERS :') then your corruption stat shouldn't be too high yet anyways. For my game, corruption stat happens on mid - major choices in the game. And while I plan some changes to your characters personality, the environment as time goes on, and the games ending, it will still follow a similar path.
Corruption is a hidden stat for now. I might change that if too many people don't like it, but for now I think it works better as a hidden stat.
Yes you can lower arousal (once per day) by masturbating. It also raises your acceptance slightly so you're more willing to do sexual actions. Also considering changing the acceptance as it's pretty easy to raise right now, but its low on my list of priorities for now.