I'm not sure specifically as there could be many novels with such a title. It might be about a mafia king who falls in love for the first time, perhaps facing conflicts between his mafia world and his new - found love.
In most cases for this kind of novel, the mafia king is the central male character. He is usually portrayed as powerful, dominant, and a bit of a mystery. His first love, let's say a young woman, could be from a different background, maybe she's a simple girl who works in a normal job or is a student. There could also be other characters like the king's right - hand man in the mafia who might have an opinion on his relationship, or the girl's friends who are worried about her getting involved with a dangerous mafia figure.
They also show the hierarchical structure. The bosses are at the top, making decisions, and the lower - level members have to follow orders without question. In many mafia novels, there are descriptions of how power is maintained and transferred within the organization. Like in 'Gomorrah', we see how new leaders emerge and the old ones are either overthrown or die in the process. This shows the cut - throat nature of the mafia world.
There's no way to know exactly who the two kings are without more context. They could be fictional characters created for the story, or they could be based on historical kings from different regions.
I recommend the novel " Peerless Beast King ". This was a story about a gang leader who was reborn into a different world. The protagonist was reborn in the body of a good-for-nothing youth. In order not to let the owner of the body continue to be bullied, he began to cultivate the secret recipe of the beast race and became the king of a generation. The story was compact and interesting, with many ups and downs. I hope you will like this novel!
Some other names that would be suitable for mafia stories are 'Mafia Riddles', which implies the mystery and puzzles associated with the mafia. 'The Forbidden Mafia' gives the idea that the mafia is something that is off - limits or not supposed to be known. 'Mafia's Trail' could be used to suggest following the path or actions of the mafia, like a detective might do in a story. These names can add intrigue to your mafia story.