Spoilery cause it will happen much later in the novel
"something" will happen to latina that will cause her to leave dale (something with her demonic presence) and would never meet dale ever again
dale knowing this would do john wick do
the clue is on the title, but to be exact, he's not defeating the maou, he's annihilating them, there's multiple maou (8 if I'm not wrong) and he is destroying almost all of them (minus the last one, but that would be another spoiler) and one of the maou is killed with only dale death aura
Great! I thought for a second there that the LN had some kind of a dumb ending by being so focused on the relationship between the two of them and then having them separated forever for some random reason.