The FBI (Federal Bureau of Investigation) is the domestic intelligence and security service of the United States, and its principal federal law enforcement agency. Colonel Lancelot Grey was the said to be the finest member of the FBI due to his master marksmanship and eventually his daughter, Jennifer Grey joined the agency as well and became one of its finest agent's as well due to her father's marksman training.

While travelling in America, the trio Shio Sakaki, Christopher Eclair and Mycroft often found themselves hired by the FBI and did numerous work for them such as bodyguarding and protecting certain individuals. However all three eventually abandoned the FBI when Sakaki turned on Eclair and Mycroft as he came to disagree with their methods. Sakaki eventually left America and returned to Japan where he joined Ryōzanpaku while Eclair and Mycroft joined Yami.