The theme of transformation is also common. Lucifer may change due to his relationship with his mate, whether it's in his personality, his goals, or his view of the world. And the struggle between good and evil within Lucifer, influenced by his mate, is another recurring theme. For example, his mate might encourage him to use his powers for good instead of evil.
One common theme is redemption. Since Lucifer is often seen as a villain in Supernatural, many fanfictions explore the idea of him finding redemption through his relationship with his mate. Another theme is power. The combination of Lucifer's power and the role of his mate in relation to that power is often explored.
Love against all odds is a very frequent theme. Given Lucifer's nature, the idea of him falling in love with a mate and their relationship surviving the various challenges in the Supernatural world is a popular one. Also, there's the theme of destiny. Fanfictions often play with the idea that the mate is part of Lucifer's destiny, either to save or damn him.
One common trait is strength. Whether it's physical, mental, or magical strength. They need to be able to stand up to Lucifer in some way. For example, if it's an angel as his mate, they would have significant angelic powers.
A common theme is the battle between good and evil. In both Supernatural and Lucifer, this is a central concept, and fanfictions often explore it further. For example, how characters are tempted by evil or strive to do good in difficult situations.
Redemption is often explored. In Supernatural, many characters are on a journey of redemption, and when Lucifer is added to the mix, the idea of whether he can be redeemed or not becomes an interesting plot point. For example, some fanfictions show Lucifer being influenced by the Winchesters' sense of justice. Another common theme is the disruption of the natural order. Lucifer's presence in the Supernatural universe throws a wrench into the already complex balance of good and evil, heaven and hell, that exists in the series. This can lead to all sorts of chaos and interesting story developments.
Redemption is also a theme. Some fanfictions might depict the female Lucifer trying to atone for her past wrongs or find a way to be something other than what she was originally created to be. This could involve her interactions with the main characters like Sam and Dean. She might try to help them in their battles against evil as a form of self - redemption. It often makes for an interesting character arc.
One common theme is the clash of powers. Lucifer has his own set of demonic powers and in the Supernatural world, there are various powers like the Winchester brothers' hunting skills and the angels' powers. So, how these powers interact is often explored.
Power struggles are common. Both shows deal with powerful beings, so in the crossovers, there's often a fight for dominance between the characters from each universe.
One common theme is redemption. Often, the presence of a soulmate makes Lucifer question his actions and strive for redemption. Another theme is the power of love. The connection with the soulmate is so strong that it can overpower Lucifer's demonic nature. And also, there's the theme of fate. It shows that even a powerful being like Lucifer is bound by the concept of a soulmate which is pre - determined by fate.
In some fanfictions, it could be a powerful angel. Since Lucifer was an archangel, an equally powerful angelic being might be seen as his mate, perhaps one with a unique connection to him from before his fall.
Love against all odds is also a prevalent theme. In many of these fanfictions, Lucifer's nature as a somewhat 'evil' or at least complex character means that his relationship with his mate is often frowned upon by others. So, the love between them has to overcome many obstacles. It could be other supernatural beings trying to break them apart or the mate having to come to terms with Lucifer's past deeds. This theme adds a lot of drama and tension to the stories.
Another theme is power dynamics. Lucifer is a very powerful being, and fem Harry usually has her own set of powers or qualities. So, how they balance the power in their relationship is often explored. For example, in some fics, Harry might be initially intimidated by Lucifer's power but then learns to hold her own.