Nagasaki

Nagasaki was a pre-War city in Japan.

Background
In the Fallout 4 intro, Nate's spoken narrative explains that the United States ended World War II by dropping atomic bombs on Hiroshima and Nagasaki in 1945.

Appearances
Nagasaki is mentioned only in Fallout 4.

Behind the scenes
The codename for the real world nuclear bomb that was detonated over the Japanese city of Nagasaki was "Fat Man" which matches an in-game weapon.