The only reason Nacht didn't kill him is because the mangaka wanted to illustrate the juxtaposition between her and the demon girl who just killed Hausmann four pages later, but it doesn't work because she's already killed like 20 people in the forest where she met Aisha and later in the cave, so there's no reason she wouldn't here after he just threatened Aisha's life. So what if Aisha likes the city? Is one noble's dead henchman going to change her ability to enjoy life here? If this place is so important to her, shouldn't you be uprooting all the corrupt nobles and killing them to make it a better, safer place to live? Not sure I agree with the leniency here, purely because of the inconsistency.