Power is a major theme. Two Lucifers would bring a lot of power into one story, and it can be about who has more power or how they use their power together.
The novel Battle Through the Heavens could be exempted from reading. This novel was written by Tian Can Tudou. It described how after the young Xiao Yan suffered all kinds of blows, he suddenly obtained the help of a wisp of a ghost and opened a brand new door. The story took place in a world of battle aura. There were no fancy magic spells, only battle aura that multiplied to the peak. If you want to read the novel Battle Through the Heavens, you can skip reading the full text in the link provided.
In the world of 'lucifer meets lucifer fanfiction', a common plot could involve a clash of egos. When two such powerful and complex characters meet, there's bound to be conflict. Some stories may also explore a romantic or at least a deeply emotional connection between them, as they are essentially the same being in different forms, and this connection can be both fascinating and disturbing at the same time.
I'm not entirely sure specifically what 'lucifer fiction' refers to. It could potentially be a genre of fictional works that somehow involve the concept of Lucifer, perhaps in a religious, mythological, or even a more creative and fictionalized context.
Lucifer can be a good comic depending on your preferences. If you enjoy dark and mythical themes, it's likely to appeal to you. The character development is strong, and the world-building is immersive.