The talk of sins on the dash inspired this. But whether its as the Seraphim Lucifer/Lucy or as the Devil who got two more names Satan/Satania, though everyone sticks to her original angel names, even God does, the Devil has always been the embodiment of two sins Pride and Wrath.
What they dislike, they dislike, there's no changing that about them. Moment something angers them, they don't try to control their anger, they do the natural thing for them, act on it but no in the sense of losing themselves. When they're angry, they focus all of their wrath on the source of it. Which is kind of what led to them getting kicked out of Heaven to begin with, picked a fight with God because they could no longer stand protecting the humans who didn't deserve protection, it went against their pride.
Which is another thing as an angel they took Pride in their job, destroying the forces of Hell, forcing them back to where they came from and protecting humanity while also judging those who collude with the forces of hell. But there was one thing that always urked them. The things people do in the name of 'God'. God believed in letting people live freely make mistakes, learn from such mistakes. The Devil though God is their best friend does not believe that includes protecting the ones who make the worst mistakes. They should be killed.
On a less serious note though because that disagreement going nowhere, the two just agree to not fight over the matter after all the time the Devil spent rearranging Hell. The easiest way to trigger the Devil's pride is to forget about them or what they are. They get so annoyed they decide to make it so they'll never forget in some fashion. Another way is to claim anything that belongs to them as yours if they never said you could have it. Its basically trying to steal something right in front of them, they won't let it slide.
That said their prideful nature why they have zero problems being blatantly obvious. The only one on their level is God so no reason to lie about who or what they are. Even when taking on a human appearance, they still use their real name. Not really caring if people realize who they are or not. Well by human appearance its just a red haired female without the horns of their usual appearance. So not much different than usual for them.