Well, likely the main theme would be the duality of good and evil. If a character is both god and satan, it shows the struggle between these two extreme forces. Another theme could be power. Being in such a dual role would involve a great deal of power, and how that power is used or misused.
I'm not sure specifically which novel this refers to. It could be about a complex character who has qualities that are both divine and devilish. Maybe it's a story exploring the duality of human nature, where the protagonist is seen as both a savior and a bringer of chaos at different times.
In the story of God and Satan, the two most prominent characters are, of course, God and Satan. God is the all - powerful, benevolent being who created the universe and everything in it. He is the source of love, justice, and mercy. Satan, originally an angel named Lucifer, rebelled against God out of pride. He now tries to tempt humans into sin and turn them away from God. Their relationship is one of opposition, with God trying to save humanity from Satan's wiles.
One such novel could be 'American Gods' by Neil Gaiman. It involves a lot of complex characters with god - like and otherworldly qualities. Another might be 'Good Omens' which has elements of angels and demons, somewhat related to the idea of god and satan. And 'The Master and Margarita' also has elements that play with the concepts of the divine and the devilish.
I don't have enough information to say who the main characters are. Since I haven't read it, it could be the girl mentioned in the title or other characters that are related to her in the story.
I'm not sure exactly as I haven't read it in detail. But it might be about a character who is neither like a goddess in terms of being perfect and all - powerful nor like Satan in being purely evil. Maybe it's a story of an ordinary or complex character in a unique fictional world.
One key theme could be redemption. If Satan is presented in a humane light, there might be elements of him seeking redemption or at least being on a journey that could lead to it. Another theme might be the relativity of good and evil. By humanizing Satan, the novel may be challenging the fixed notions of good and evil we usually hold.
One similar novel could be 'American Gods' by Neil Gaiman. It deals with gods from different mythologies living in modern - day America, and many of these gods have complex and often morally ambiguous natures. Another might be 'The Picture of Dorian Gray' where Dorian starts as an innocent and beautiful young man (almost god - like in his purity and charm) but gradually descends into a life of sin and corruption, becoming something more like a satanic figure.
One common theme could be the exploration of power. Since Satan is often associated with power, in 'female satan fanfiction', the female character representing Satan might be depicted as having great power and using it in different ways, whether for good or evil.
Common themes in a satan love story include power dynamics. Satan is often associated with power, so in a love story, there could be a power struggle between the lovers. Another theme is the blurring of moral boundaries. Love can make one overlook the immoral actions of Satan or his followers, leading to a complex exploration of ethics in the story.
One common theme could be the struggle between good and evil, with Percy in the role of Satan having to deal with his own dark nature while perhaps still having some remnants of his former self. Another might be power and corruption, as Satan is often associated with great power in many mythologies.