Kazui is to be the heir of an assassination group called "Kill Mail" in the fairly tale realm. They carry out the villains or clients dirty work. Even though his father (the boss) keeps giving him assassin missions, Kazui hates being an assassin and just wants to live out a normal life.
Since he's been failing at his job, his father decides to give him some help by placing the two top best as well as most annoying assassins at his side! Kazui's days of suffering begins!