The Devil's Sea, also called the Formosa Triangle, is located off the coast of Japan in a region of the Pacific around Miyake Island, about 110 miles south of Tokyo. Like the Bermuda Triangle, the Devil's Sea doesn't appear on any official maps, but the name is used by Japanese fishermen. The area is known for strange disappearances of ships and planes - at least by those in the United States.
Another myth is that, like the Bermuda Triangle, the Devil's Sea is the only other area where a compass points to true north rather than magnetic north (more about this later).
One popular theory is that volcanic activity around the area, particularly an underwater volcano, could be responsible for the disappearances.
Contrary to several claims, neither the Devil's Sea nor the Bermuda Triangle is located on the agonic line, where the magnetic north equals the geographic north. The magnetic declination in this area is about 6 degrees. As is the case with all things mysterious, there are many theories regarding the Devil's Sea. One of the most prominent is that there is a large amount of volcanic activity around the area, and an underwater volcano could obliterate a ship without a trace.