Amphisbaena no Kuchizuke

https://www.cmoa.jp/title/370983

Italy, 1948. Blue, a "Double Poison Dragon," is forced to carry out assassinations daily, her abilities exploited by the mafia. One day, she is ordered to assassinate a young man named Kalman, but the mission fails. He himself is destined to be killed, but Kalman is also a Double Poison Dragon, and his life is spared. He then decides to fight the mafia in search of freedom.