With the law enacted 20 years ago monsters penetrated human society. However, the fundamental difference between people and demons persists and there is a lot of protest movement, so the government dedicates an entire city of the Kanto prefecture as a monster 's living area with full autonomy - Baharihara City.
Main heroine Saki lives this city with her vampire father and human mother. She gets caught up in the rapist attacks and discovers powers of an old god inherited from her father vampire. However, the government of Baharihara City can't tolerate rivalry and plans to assassinate Saki. So starts the battle over Saki and the Old god in the Baharihara City.

[From vndbreview]