The Mafia's Assassin (Karma x Nagisa)

Nagisa is a top notch assassin, he never walks away from a job. Even one night at a bar a member of the mafia gives him an assignment to kill one of the most deadliest people around and to join the mafia for $1,000,000,000. When Nagisa shows up at the headquarters of the mafia he gets partnered with a man called Karma. How will Karma & Nagisa's relationship turn out and will they be able to kill this person?