Meanwhile, after you've developed a certain kind of stupid scorn for him (having utterly skipped the fangirl phase) you meet satan, who develops an interest in you and you end up keeping your relationship a secret.
On everyones birthday at noon, one word appears on their skin, depicting their career or purpose in life. On your birthday, youre staring at the clock showing Family and friends are gathered around for your reveal.
Others have commented the assassin is a time traveller. Time travel has nothing to do with it! Affect an unrelated thing in such a way that the knock on effect leads to the death of the intended victim.