TISTA - Manga

Taken from baka-updates: The series is set in New York City, and the main character is a young girl named Tista. In the day, she is a shy, introvert, church-going student whose ambition in life is to become a teacher. At night, she assassinates criminals as her alter-ego, Sister Militia. A special feature of her eyes give her the ability to spot a target from miles away, be it moving or stationary. Once she's spotted her target, it's one-shot one-kill. Why is Tista killing for the church? What happened to her father? How did she get those eyes?