Phantom: The Animation - Season 1

Zwei traveled to a new city to start a new life. There he sees the girl of his dreams, Ein, for the very first time. Strangely, he spots her from 500 meters away, while she's crouched behind a military issue sniper rifle picking off mobsters. Soon Zwei's uncanny alertness comes to the attention of Ein's employers, and he's given a simple choice: train to become an assassin, or be marked as Ein's next target.