In Succubus Contract, MC is a young 18-year-old man. One day he goes to a club with his buddy Tom. They plan to relax, drink, and hopefully meet some women. When they get there MC meets a woman who seems normal and inconspicuous. After drinking and eating together they appear to be developing a closer relationship.
The fact is this woman is a succubus, which is a sexual demoness. MC wants to have sex but doesn't know she is a demoness who is counting on him having sex with her. She offers him terms for this and he agrees (and seals the deal with a sexy kiss), not realizing there are hidden meanings in her words. So, they do the deed and he goes to sleep. But he wakes up as a girl! Now you must go through life and the upcoming adventure in this new body and see what happens.