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.