The themes in 'batman vs joker graphic novel' are complex. There is the theme of morality. Batman adheres to a strict moral code, while the Joker has no such constraints. This creates a contrast that drives the story. The theme of the power of insanity is also present. The Joker's insanity gives him a certain kind of power, and Batman has to find a way to counter it without losing his own sanity. Additionally, the theme of the city as a battleground is important. Gotham is where their fight takes place, and it represents the struggle between chaos and order on a larger scale.
The main characters are, of course, Batman and the Joker. Batman is the Dark Knight, a vigilante who uses his skills and gadgets to fight crime in Gotham. The Joker is his arch - nemesis, a deranged criminal with a warped sense of humor.
I don't know for sure. The ending of such a manga can be quite unpredictable and might not have been revealed yet. You could try discussing it with other fans to get their speculations.
I'm not really sure if they end up together. Different people might have different interpretations. Maybe you can dig deeper into the manga and form your own conclusion.