My Guardian Devil (Karma x Reader)

(Y/N) (L/N) has never had an easy life, especially being the top assassin in the number one assassin school in America, but she sticks it out for the sake of someone very important to her. So when she is given the mission to go to Japan and assassinate the monster responsible blowing up the moon, known as Koro-Sensei she is of course reluctant to accept but subjects when the award money could be her key to a better life. Will she succeed in killing the unkillable monster or will a certain sadistic redhead give her a new purpose and change her life for the better.