Ordinary, cute girl loses contact with her older sister who was reporting on some demonic cult. She becomes worried and starts looking for her. Player's action determine whether she saves her sis and reaches Happy End or is corrupted and turns into evil Succubus. Game is not particularly long but it has 12 different endings.
Someone asked about that game of Marsa I mentioned earlier so decided to post pics from it. You can download it here on pixiv: https://www.pixiv.net/artworks/93569107
Game is free to download, can be played through browser and once you launch it you pick if you want English or Japanese version. (you can log through google/twitter/apple account if you don't have pixiv account to download) If you are interested in it then I really suggest you don't view pictures in this gallery and just download and play the game.
BTW Marsa created two other similar games. One is about corruption of office lady who started visiting suspicious esthetician. Second is set in school where sexy new teacher starts working and corrupts students and other teachers. Both are Succubus TF and both can be found on author's pixiv website.
If you wanna follow or support author: Pixiv: https://www.pixiv.net/users/375450 Fanbox: https://www.fanbox.cc/@marsa Twitter: https://twitter.com/marsax_
Are these in order? The impression I get is they are not, but I suppose it could just be that it's simply hard to follow with no text to keep track of things.