This is the best succubus game in existence.
The plot is simple. You are trapped in the house of 3 succubi. The one that claimed you likes to let her prey stew in fear before she kills them. This gives you time to try and find your way out, which involves researching demonology, finding artifacts, sacrifficing other people to save your life, etc. Make one misstep on that path and you die in a hentai-scene. Good luck escaping.
The succubi are evil, cruel, scary and insanely hot. There is no "breaking the succubus" or "true love endings" etc. There are 3 basic succubi, but you can summon many more in rituals. They are all evil or indifferent, there are no "good" succubi. They are predators and humans are helpless food and they enjoy that fact a lot. The best you can do is run away. It's not a "sex on defeat" type of game either, there are no battles. You evade an encounter, talk your way out of it, or you die. That's it. There is a lot of scenes with music and voiceover, secrets, and an extremely difficult path to "win", which just means you escape with your life. A "win" is pretty much impossible without a guide or replaying it a hundred times, mapping out what succubi do at any given time of day and planning around all that.
The game is a perfect storm that makes it the one game I replayed the most. It does an excellent job of building an atmosphere of dread, which only magnifies the experience. It has some drawbacks, but it's still the best there is.
That being said, there are some negatives. One of the main characters is a "loli grandma" and there are also a few loli and shota scenes in there. I dislike that, but that's the Japanese for you. I just skip those scenes. If you hold "a" during a scene, it will play super-quick and if you encounter the same scene again, you can just skip it. I wish there was a mod that let me just auto-skip those scenes. Still, the rest of the game is so amazing that it is worth working around these problems. There is also mind control, death and such, but that comes with the nature of the game. There is a futa scene and 2 vore scenes, but they are avoidable if it's a problem for you. All the scenes are avoidable if you know what you are doing. Escaping the house actually requires you to avoid all but 2 scenes.
To sum up, best succubus game ever. Possibly best porn game ever. Try it. There is one other succubus game that is a close second, but I'm not allowed to mention it here. If you want to know what it is, I talk about it on page 41 of the discussion.