Ceritanya lumayan.

This is a story about the ultimate killer from chronos number, called Black Cat. Chronos Number is a secret organisation that secretly rules 1/3 of world's economy.
One day, Train Hartnet was assigned to eliminate the Torneo's ultimate weapon. However, because of his encounter with Saya, so far the cutest girl in this anime, somehow he lost his killing instinct and decide to help the torneo ultimate weapon instead of killing her.
To make it short, Train quit the chronos number, but somehow he still couldn't live peacefully because of his ability attracts many people who want his power.