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.
Themes are important too. Things like redemption, the nature of good and evil, and the struggle against fate often come up in these crossovers. For example, Lucifer's journey towards possible redemption might be affected by Constantine's more black - and - white view of the world, and how they resolve that can be a really interesting part of the story.
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.
One great Constantine Lucifer crossover fanfiction is 'The Devil and the Exorcist'. It has an interesting plot where Constantine and Lucifer team up to deal with a powerful demonic entity that threatens both their worlds. The character interactions are well - written, with Constantine's cynicism contrasting Lucifer's charm.
One idea could be that Alec, from the Malec universe, stumbles into Lucifer's realm while on a mission. He's initially confused and on guard. Lucifer, being the charming devil he is, tries to make a deal with Alec. But Alec, being true to his Shadowhunter values, refuses. This could lead to an interesting dynamic where Lucifer is intrigued by Alec's integrity and Alec is both repelled and fascinated by Lucifer's world.
In some comic storylines, Constantine's sexuality is ambiguous or not clearly defined. It depends on the specific interpretation and version of the character.
In some comic storylines, Constantine's sexuality may be explored or depicted in a way that suggests he could be gay, but it's not a consistent or definitive aspect across all of his appearances.