Iceman

About

Iceman was a member of the Port Mafia's Flags and a hit man. The second-most senior in the Flags after Piano Man, Iceman's job in the Mafia was to kill. After his kill ratio became higher than the average combat-type ability user, the Mafia placed their trust in him. At one point, Iceman was apparently sent but failed to assassinate Chūya, then the Sheep King, who would later become his comrade as part of the Flags.

(Source: Bungo Stray Dogs Wiki)