Marco Amoretti is a former American Imperial Navy Petty Officer. Due to the events that happened during "Project Sunset" - a covert CIA operation during World War IV - he became into a psychotic serial killer.
In Japan he attacked six people (one survived, five died) by skinning them alive. Due to this incident the CIA tried to get Amoretti killed by Section 9 member Batou who, during his time as a JGSDF Ranger, also took part in "Project Sunset". But Amoretti was captured by Batou instead and was transferred to the American Empire.