Just a suggestion;
Why not add the Hero to the list. Have him take a TS/Gender Swap poison when they are captured so that as he is being sexually tortured by succubus in the dungeon, he is steadily losing his masculinity. Though it will probably flag the game as Yaoi/Futanari for this, but for "her" first corruption, "she" will have a developing pussy and dick that has shrunk down to almost the size of a clitoris, and by the end of "her" scene the last remaining vestiges of "her" physical masculinity will forever disappear, she will than look in horror, not only from the fact that she is now forever changed to being female, but also seeing her former party members corrupted forms and her body getting involuntarily wet with excitement of being corrupted like them, having had her former male member purposefully ignored during her torture so that she would have only the faintest memories of pleasure that a man can experience, all she can do at that moment on is wait in expectation of the pleasures of a woman that her former party members are so enthralled in. A better punishment to such a frustratingly condescending, arrogant, and self-entitled man to suffer from than just sexual torture.
This is just my fetish for Gender Swap, where the formerly male character has to live with there new body in the sexual environment they are in, even adding to the corruption as the character will experience the brain frying experience of being sexually broken.
Also it would be nice if each of the girls had different corrupted form, instead of all just being succubus, though we have only the one fully corrupted character so I don't know if you have already decided on one or the other.