She is Shadow

Her family is murdered. She is sold to a mafia organization, making her determined revenge. She called herself Shadow. Noone knows her realname. She is a hitman born to a Black Demon mafia organization, under the pseudonym Cleo Anatasia Veendra. She never realized that she was the subject of a successful experiment test conducted by her own master's man, it healed his wounds within seconds, as having an amazing experiment made her an Interpol fugitive.